Imaamah (Turban), Kufi (cap), IzAar (loincloth), 
Thawb (long shirt or Qamis) on praying bearheaded (without a Turban or Kufi) wearing the clothes of the unbelievers

We glorify Allaah and ask blessing on and salute on His noble Prophet, his companions and those follow him in upholding the cause of the right religion. It is great Mercy of Allaah (s.w.t.) that He has showered with most valuable treasure in this earth, that is Islaam, a true guidance.

(This tafseer is Agreed upon by Ibn Kathir, Al-Qurtabi and At-Tabari)

The Holy Qur'ân, Surah #3;Ayah #31
"Say (O Muhammad SAW to mankind): "If you (really) love Allâah then follow me (i.e. accept Islâmic Monotheism, follow the Qur'ân and the Sunnah), Allâah will love you and forgive you of your sins. And Allâah is Oft Forgiving, Most Merciful."

The Holy Qur'ân, Surah #33;Ayah #21
"Indeed in the Messenger of Allâah (Muhammad SAW) you have a good example to follow for him who hopes in (the Meeting with) Allâh and the Last Day and remembers Allâh much."

The Holy Qur'ân, Surah #42;Ayah #52
"And thus We have sent to you (O Muhammad SAW) Ruhan (an Inspiration, and a Mercy) of Our Command. You knew not what is the Book, nor what is Faith? But We have made it (this Qur'ân) a light wherewith We guide whosoever of Our slaves We will. And verily, you (O Muhammad SAW) are indeed guiding (mankind) to the Straight Path (i.e. Allâah's religion of Islâmic Monotheism)."

The Holy Qur'ân, Surah #59;Ayah #7
"And whatever the Prophet gives you, ACCEPT IT and whatever he forbids you, ABSTAIN (from it)"

Sahih Al-Bukhari, Volume 9, Book 92, Hadith # 401
Narrated Ibn `Umar (Radhiallaahu Án): Rasulullaah (SallAllaahu Alayhi Wa sallam) wore a gold ring and then the people followed him and wore gold rings too. Then the Prophet said, "I had this golden ring made for myself." He then threw it away and said, "I shall never put it on." Thereupon the people also threw their rings away. Note: Look at hoe strict the Sahaba (Radhiallaahu Án) were in following the Sunnah of Rasulullaah (SAW) what ever he did they followed him.

Abu Dawud and Imaam Ahmad Bin Hanbal
On the authority of Ibn `Umar (Radhiallaahu Án) who said that Rasulullaah (SallAllaahu Alayhi Wa sallam) said "Whoso resembles a people in appearance, he is one of them." (Also narrated by Ibn Abi Shayba in his Musannaf (5:313), Ibn Hajar in Fath al-Bari 10:274 [Dar al-Fikr ed.], and Ibn Kathir in his Tafsir (8:53). `Iraqi said its chain is sound (Sahih). al-Bazzar also relates it through Hudhayfa and Abu Hurayra, Abu Nu`aym through Anas, and al-Quda`i relates it through Tawus, a chain which Ibn Hibban declared Sahih. Ibn Taymiyyah in his Iqtida' al-siratal- mustaqim (p. 82) calls Abu Dawud's and Ahmad's chain "a good chain." )

Tirmidhi (hasan), Book of knowledge; al-Baghawi, Sharh al-sunna 1:233 : Rasulullaah (SallAllaahu Alayhi Wa sallam) said "Whoever gives life to one of my Sunnahs which was eliminated after my time will receive the reward of all those who practice it without their reward being diminished"

Tirmidhi (hasan gharib), Book of knowledge:  Rasulullaah (SallAllaahu Alayhi Wa sallam) Said "Whoever gives life to one of my Sunnahs, he loves me: and whoever loves me is with me."

Al-Mundhiri, al-Targhib 1:87; Al-Hakim: Rasulullaah (SallAllaahu Alayhi Wa sallam) Said "The keeper of my Sunnah at the time my Community has lapsed into corruption will receive the reward of a martyr." 

Al-Bayhaqi, al-Sunan al-kubra 5:245; Ibn al-Athir, Usd al-ghaba 3:341; Dhahabi narrates that Abdullah Ibn `Umar (Radhiallaahu Án), used to dismount in order to walk on the exact same spot the Rasulullaah (SallAllaahu Alayhi Wa sallam) had put his steps.  Note: This is how strict the Sahâbah (RadhiAllaahu Ánhuma) were in following the Sunnah of Rasulullaah (SAW)!  And they understood the Deen better than us. 

The Imaamah (Turban)

Sahih Al-Bukhari Volume #1 pg#536: Ibn Abbas (Radhiallaahu Án) reports that Rasulullaah (SallAllaahu Alayhi Wa sallam) addresses the Sahâbah while wearing a black turban.

Sahih Al-Bukhari Volume #1, Book 4, Hadith # 204
Narrated Ja'far bin 'Amr: My father said, "I saw the Prophet (SallAllaahu Alayhi Wa sallam) passing wet hands over his turban and Khuffs (leather socks)."

Sahih Al- Muslim Book 2, Hadeeth # 0535: Narrated Bilal ibn Rabah: Rasulullaah (SallAllaahu Álayhi Wa sallam) wiped over the socks (khufs) and turban (Imaamah). In the hadeeth transmitted by Isa ibn Yunus the words are: 'Bilal narrated it to me.

Sahih Al- Muslim Book 7, Hadeeth # 3146: Narrated Jabir ibn Abdullah: Rasulullaah (SallAllaahu Álayhi Wa sallam) entered Mecca. Qutaybah  stated that he entered Mecca in the Year of Victory, wearing a black turban, but not wearing the Ihram. (also reported by Tirmidhi vol.1 pg 304 and Ibn majah pg205)

Sahih Al- Muslim Book 7, Hadeeth # 3148: Narrated Amr ibn Hurayth (RadhiAllaahu Án) Rasulullaah (SallAllaahu Álayhi Wa sallam) addressed the people (on the day of the Victory of Mecca) with a black turban on his head.

Sunan Abu Dawood Book 1, Hadeeth # 0147: Narrated Anas ibn Malik: I saw Rasulullaah (SallAllaahu Álayhi Wa sallam) perform ablution. He had a Qutri turban. He inserted his hand beneath the turban and wiped over the forelock, and did not untie the turban.

Sunan Abu Dawood Book 32, Hadeeth # 4068: Narrated Abdur Rahman ibn Awf: Rasulullaah (SallAllaahu Álayhi Wa sallam) put a turban on me and let the ends hang in front of him and behind me.

Tirmidhi from the book Shamaa'il Tirmidhi pg #108 Hadeeth # 109: Amr bin Hurayth (Radhiallaahu Án) relates that Rasulullaah (SallAllaahu Álayhi Wa sallam) gave the khutbah and he was wearing a black turban on his head.

Abu Dawood and Tirmidhi: 
Roknah (Radhiallaahu Án) reports that Rasulullaah (SallAllaahu Álayhi Wa sallam) said "The distinction between us and the polytheists is the turbans over our caps. "
Note : Also quoted by Al-Tabrizi in his Mishkat Al-Masabih and this clears up the false notion that this was just the way of the Arabs and not a particular practice of Rasulullaah (SAW) and this shows us that we should wear caps under our Imaamah's to differentiate from the Sikhs and other Kufar who wear turbans but without caps under them.

MISHKAT page #377 and also reported by Baihaqi in Shuabul Imaan: Ubadah (Radhiallaahu Án) reports that Rasulullaah (SallAllaahu Álayhi Wa sallam) "Make a practice of tying Turbans since it is a hallmark of the angels."  
Note: Here Rasulullaah (SAW) is even advising others to wear the Imaamah!

Tabrani: Musa Ashari (Radhiallaahu Án) narrates that Jibraeel would come to Rasulullaah (SallAllaahu Álayhi Wa sallam) wearing a turban.

Haakim cited in the book Mustadrak Haakim vol34 pg#540
Aa'ishah (RadhiAllaahu Ánha) reports a on the occasion of the battle of the trench a man came to Rasulullaah (SallAllaahu Álayhi Wa sallam) wearing a Turban and when she asked Rasulullaah (SallAllaahu Álayhi Wa sallam) about this man he  informed her this was Jibraeel. (Haakim has declared this hadeeth to be SAHIH)

At-Tabrani and Haakim  reports this to be reliable Hassan
(Also quoted in Tabarani's al-Mu`jam al-kabir (1:162), Bazzar's Zawa'id, al-Hakim's Mustadrak (4:193), al-Khatib al- Baghdadi's Tarikh Baghdad (11:394), and Ibn `Asakir's Tahdhib tarikh dimashq al-kabir (5:178): Ibn Abbas (Radhiallaahu Án) reports that Rasulullaah (SAW) said "Adopt the Turban as it will increase your Hilm ( good character, intelligence, patience)." 

Al-Munawi said in the commentary on Tirmidhi's al-Shama'il:  "The turban is a Sunnah, especially for prayer and for self beautification, because of the many narration's concerning it."

Shaikh Muhammad Ibn Jameel Zino (Imaam Muhammad Ibn Saud Islamic University) in his book Al-Shamail Al-Muhammadiyyah on page #106): Headwear are symbols of nations and many Muslims imitate the unbelievers by wearing their head wear. In fact, covering their heads with a Turban, or even a scarf, is better for them and further from resembling the unbelievers.

From his commentary of Mishkat vol#1 pg#630): "The holy Prophet (SallAllaahu Álayhi Wa sallam) used to wear a Turban and he said that the angels also wear it in the heavens and the turban protects the head and adorns the face."

Ibn Hajar Al-Asqalani (Rahimahullaah) mentioned in FathulBaari pg#491 and 493: That Imaam Bukhari and Imaam Muslim both wore Turbans.
Note: that they were not Arabs but took this practice as the Sunnah of Rasulullaah (SallAllaahu Álayhi Wa sallam) .

Ibn Al-Jawzi and Ibn Al-Qayyim (In Rawdat al-muhibbin p. 225): "Hasan al-Basri (Rahimahullah) wore a Black Turban"

Imaam Nawawi (Rahimahullah)( quoted from the biographical notice for Imaam Nawawi in the Reliance of the Traveller): "Imaam Nawawi all his life possessed only a thawb (long shirt) and a turban"

The Izaar

Sahih Al-Bukhari Volume 7, Book 72, Number 678:
Narrated Abu Huraira (RadhiAllaahu Ánhu): Rasulullaah (SallAllaahu Álayhi Wasallam) said, "The part of an Izaar which hangs below the ankles is in the Fire."

Sahih Al-Bukhari Volume 7, Book 72, Number 681: Narrated 'Abdullah bin 'Umar (RadhiAllaahu Ánhu): Rasulullaah (SallAllaahu Álayhi Wa sallam) said, "While a man was dragging his Izaar (lower cloth) on the ground (behind him), suddenly Allaah made him sink into the earth and he will go on sinking into it till the Day of Resurrection."

Sahih Muslim: Abdullah Ibn Umar (RadhiAllaahu Ánhu) said "I passed by the Rasulullaah (SallAllaahu Álayhi Wa sallam) while my lower garment was hanging down, so he (SallAllaahu Álayhi Wa sallam) said ' Abdullah, raise your garment.' I raised it, and he told me to raise it further, and I did so.  As I was still trying to find the best manner, someone from the people asked where it should reach, and he (SallAllaahu Álayhi Wa sallam) replied ' Halfway down the shins.' "This Should clears up the feeble excuse of people saying that they hang their pants and clothes down but not out of pride, here this is Ibn Umar (RadhiAllaahu Ánhu) a famous Sahâbahi, surely he has more ikhlaas than us but still Rasulullaah (saw) told him to raise it.  And Rasulullaah (saw) has shown us that our lower garment should reach the middle of the shin.

Tirmidhi (from the book Shamaa'il Tirmidhi pg #115 Hadeeth #114): Salamah bin Akwa (Radhiallaahu Ánhu) says "Uthman (Radhiallaahu Ánhu) wore his lungi (Izaar) till the middle of his shin and said 'This is how Rasulullaah (SallAllaahu Álayhi Wa sallam) wore his Lungi" (We should note on how the Sahâbah were strict in following the dress code of Rasulullaah (SAW)!  And they did not have pride but still stuck to the Sunnah of Rasulullaah (SAW)!

Tirmidhi (from the book Shamaa'il Tirmidhi pg #115 Hadeeth #114): Hudhayfah bin Yamaan (Radhiallaahu Ánhu) reports that "Rasulullaah (SallAllaahu Álayhi Wa sallam) caught the shin of my leg and said" this is where the lungi should reach and if not then a  little further down but if not then it has no right on the ankle." (meaning that it should be above the ankle!)

Abu Dawood and Ibn Majah reported this hadeeth to be fully authentic: Abu Sa'id Al-Khudri (Radhiallaahu Ánhu) reported that he heard Rasulullaah (SallAllaahu Álayhi Wa sallam) say "The way for a believer to wear the lower garment is to have it halfway down his shins, and he is not guilty of sin if it comes halfway between that and the ankles, but whatever comes lower than that is in hell (and he repeated this three times).  On the day of resurrection, Allaah (swt) will not look at him who trails his lower garment conceitedly." (here we should see the Rasulullaah (SAW) has shown us the way for a believer to wear the lower garment is to have it halfway down his shins and then Rasulullaah (saw) allowed it to be from the middle of the shin half way to the ankle but what excuse do we have to drag our pants past our ankles?)

Sahih is Reported by Imaam Ahmed Bin Hanbal: The Prophet (SallAllaahu Álayhi Wa sallam) saw a man with a long waist-shirt (Izaar) and ordered him to have his Izaar halfway up his shins; the man gave the excuse that he had a defect in his ankles, so the Prophet (SallAllaahu Álayhi Wa sallam) said, "All of Allaah's creation is handsome." (Sahih-Ahmad and again this shows the clothing can not go under the ankle even if it is not out of pride!)

Ibn Hajar (Expresses his view in the book Fath-al-Bari)
In which he sates that it is not permissible for a garment to extend below the ankles.  He says: "Al-Qadhi Ayadh quoting the consensus of the Muslim Ummah, states that this prohibition is limited to men only." 

Shaikh Muhammad Naasir ad-Deen al-Albaani: On the subject of people hanging their clothes past the ankle with the excuses like it is not out of pride.....the Prophet (SAW) saw a man with a long waist-shirt and ordered him to have his Izaar halfway up his shins; the man gave the excuse that he had a defect in his ankles, so the Prophet (SAW) said, "All of Allaah's creation is handsome." (Sahih Imaam Ahmad and others. This phrase is actually of Qur'ânic origin from Surah Sajdah #32 ayah #7)

Ibn Qayyim(RA): states that Rasulullaah (SallAllaahu Álayhi Wa sallam) bought and wore the Izaar.

Shaikh Muhammad Ibn Jameel Zeeno (Imam Muhammad Ibn Saud Islamic University in his book Al-Shamail Al-Muhammadiyyah on page #106): "It is forbidden (to wear tight pants), because it reveals the persons private parts; and it is a way of imitating the unbelievers."

The Thowb (long shirt or gown)

Tirmidhi, Abu Dawood (and in Mishkat Vol #1 pg# 643)
Umme Salamah (Radhiallaahu Ánha) reports that the dress most liked by Rasulullaah (SAW) was the long gown (thowb). (Tirmidhi has related this to be Hasan with a reliable and authentic chain of narraters)

Sahih Al-Bukhari (Can be found in  the book Mishkat vol #1 pg #630) Anas (Radhiallaahu Ánhu) reports that the dress most pleasing to Rasulullaah (SallAllaahu Álayhi Wa sallam) for use was a green-coloured Thowb.

Tirmidhi (In the book Shamaa'il Tirmidhi Pg #61): Asmaa bint Yaseed (Radhiallaahu Ánhu) says "The sleeve of the Rasulullaah SAW)'s Thowb reached to the wrist." 

AbuDawud Book 28, Number 3869: Narrated Abdullah ibn Abbaas (RadhiAllaahu Ánhu): The Prophet (SallAllaahu Álayhi Wa sallam) said: Wear your white garments, for they are among your best garments, and shroud your dead in them. Among the best types of collyrium you use is antimony (ithmid): it clears the vision and makes the hair sprout. (Abu Dawud, Imaam Ahmad and other have transmitted this hadeeth to be Sahih with a Authentic and reliable chain of narrators.)

Sahih Al-Bukhari Volume 7, Book 72, Hadeeth # 717:
Narrated Abu Dharr (RadhiAllaahu Ánhu): I came to the Prophet (SallAllaahu Álayhi Wa sallam) while he was wearing white clothes.

The Kufi (cap)

Tabrani And Imaam Suyuti: Ibn Umar (RadhiAllaahu Ánhu) narrates that Rasulullaah (SallAllaahu Álayhi Wa sallam) used to wear a white cap (kufi). Tabrani has reported this hadeeth to be Hasan (reliable) and Suyuti has classified this hadeeth as highly authentic (Sahih) in the book Sirajul Muneer vol #4 pg#112)

Sahih Al-Bukhari Volume 2 pg #863
It is mentioned that Anas Bin Malik (Radhiallaahu Ánhu) used to wear a kufi (cap).

Tirmidhi
Roknah (Radhiallaahu Ánhu) reports that Rasulullaah (SallAllaahu Álayhi Wa sallam) said "The distinction between us and the polytheists is the turbans over our caps."

Sunan Abu Dawood Book 3, Hadeeth # 0948:
Narrated Umm Qays bint Mihsan: Hilal ibn Yasaf said: I came to ar-Raqqah (a place in Syria). One of my companions said to me: Do you want to see any of the Companions of the Prophet (SallAllaahu Álayhi Wa sallam)? I said: A good opportunity. So we went to Wabisah.  I said to my friend: Let us first see his mode of living. He had a cap (kufi).

on praying bearheaded (without a Turban or Kufi)

Shaikh Albaani (May Allaah's mercy be on him) (From Al-Qawl Al-mubin fi akhta' Al-musallin by Mashhur Hussain on page # 58 of the 2nd edition):  "Praying bareheaded is makruh (disliked)."

It is not established at all that the Messenger (sallallaahu 'alaihi wa sallam) ever prayed outside the pilgrimage with bare head, without a turban/cap. Whoever thinks he did so then he should bring the proof. If he (sallallaahu 'alaihi wa sallam) had done so, it would have been recorded. The narration attributed to Ibn 'Abbaas that the Prophet (sallAllaahu 'alayhi wa sallam) would sometimes remove his cap and place it as a sutrah in front of him is weak (da'eef). 

Shaikh Albaani (May Allaah's mercy be on him) (Al-Din al-khalis (3:214) and al-Ajwiba al-nafi`a `an al-masa'il al-waqi`a (p. 110): "All acknowledge that it is desirable for the Muslim to enter prayer in the most perfect Islaamic appearance, due to the hadeeth: "Allaah is worthier of your self- adornment" [hasan]. And it is not part of excellent attire in the custom of the Salaf to habitually bare one's head, and walk in that guise on the road and when entering places of worship. Rather, it is a foreign custom which infiltrated many Islaamic countries at the time the disbelievers invaded them and brought their habits with them. The Muslims began to imitate them in this, and they lost thereby their Islaamic personality as well as through other similar acts... Nor is it established that the Prophet ever prayed bareheaded and without a turban other than in the state of ihram, although there were plenty of occasions to report it if he did. Therefore, whoever claims that he did, let him produce the proof, for truth is more deserving to be followed."

Shaikh Albani (May Allaah's mercy be on him) goes on to explain the mistake of some brothers in Egypt who brought the proof of the permissibility to pray without covering the head by analogizing with how the head is uncovered for someone in ihraam during the pilgrimage. This is wrong since not covering the head during the pilgrimage is from the law (Sharee'ah) of Allaah. If their analogy was right then they should make it compulsory to pray without any head covering at all since it is obligatory to do so during the pilgrimage and to follow all the other restrictions of Ihraam in regular life! [Tamaam-ul-Minnah fee ta'leeq 'alaa fiqh-us- Sunnah by 'Allaamah Albaani] 

Allamah Jauzi (Allah's mercy be on him) (From Fatawa Rahimiyya 3:202 #308.): "To keep the head bare before the people is an act which is looked down upon and is against gentleness, humanness, etiquette, and gentlemanly decorum."

Hanbali Fiqh (Quoted By Ibn Qudama, al-Mughni (1994 ed.) 1:404-405): "It is mustahab to pray using a Thawb, Silwar (Sunnah pants) or a Izaar (loincloth) and a turban"

Maalik Fiqh (Quoted by Ibn Abi Zayd, al-Jami` fi al-sunan (1982 ed.) p. 228): Imaam Maalik said "The turban was worn from the beginning of Islaam and it did not cease being worn until our time. I did not see anyone among the People of Excellence except they wore the turban, such as Yahya ibn Sa`id, Rabi`a, and Ibn Hurmuz. I would see in Rabi`a's circle more than thirty men wearing turbans and I was one of them, and Rabi`a did not put it down until the Pleiades rose (i.e. until he slept) and he used to say: "I swear that I find it increases intelligence."

Shafi`i Fiqh (Quoted by Al-Misri in Reliance of the Traveller p # 122): "It is mustahab to pray using an ankle-length Thawb and a turban"

Hanafi Fiqh (Quoted by Al-Shurunbali in Muhammad Abul Quasem p #91): It is mustahab or praiseworthy to pray using "three of one's best clothes, a Thawb, Silwar (Sunnah pants), and turban or kufi" According to the Hanafi school (Al-Jazayri, al-Fiqh `ala al-madhahib al-arba`a, Kitab al- Salat p. 280-28) [among] the disliked acts (al-makruhat) in prayer are:... i`tijar, which is to tie a scarf around the head and leave the center bare;... [or] praying bareheaded out of laziness. As for praying bareheaded out of humility and submission, it is permitted (ja'iz) and not disliked.(16)

Shaikh `Abd al-Qadir Jilani (From Ghunyat al-talibin 1:14)
"It is the method or habit of orthodox or civilized virtuous men to keep the head covered."

wearing the clothes of the unbelievers

Umar Ibn Khattab (Radhiallaahu Ánhu)(Quotes by Ibn Hibban in his Sahih and Imaam Ahmad Bin Hanbal) Abu `Uthman (Radhiallaahu Án) said "Umar's letter reached us as we were in Azerbaijan saying: "O `Utba Ibn Farqad, stay away from effeminacy and the clothing of idolaters (mushrikeen)." (Ibn Hibban in his Sahih and Imaam Ahmad Bin Hanbal)" 

Ibn Taymiyya (Allah's mercy be on him) (Quoted from Ibn Taymiyya's Iqtida' as-sirat al-mustaqim (1907 ed.) p #60)
In tafseer of this hadeeth "Abu `Uthman (Radhiallaahu Án) said "Umar's letter reached us as we were in Azerbaijan saying: "O `Utba Ibn Farqad, stay away from effeminacy and the clothing of idolaters (mushrikin). Ibn Taymiyya interpreted it as an explicit prohibition for Muslims in non-Muslim countries against wearing unislaamic clothing: This is a prohibition on the part of `Umar directed at Muslims against all that belongs to the manner of dress of non-Muslims (mushrikun).

Shaikh Muhammad Ibn Jameel Zeeno (Imaam Muhammad Ibn Saud Islamic University) in his book Al-Shamail Al-Muhammadiyyah on page #105: "It is not permissible for a Muslim to wear the garments of the unbelievers, or to adorn himself with their uniforms, as a result of the Prophet (SAW) saying: 'Whosoever imitates a people becomes one of them." (Abu Dawud)

Shaikh Muhammad Ibn Jameel Zeeno (Imam Muhammad Ibn Saud Islamic University in his book Al-Shamail Al-Muhammadiyyah on page #106): "It is forbidden (to wear tight pants), because it reveals the persons private parts; and it is a way of imitating the unbelievers."

And ALLAAH knows BEST......