All praise is due to Allah and may Allah's peace and blessings be upon His messenger (saws). Verily the best speech is the book of Allah and the best guidance is the guidance of Muhammad sallallahu alaihiwasallam and the worst of affairs are the newly invented matters and every innovation is misguidance and all misguidance is in the fire. (Sahih Muslim Eng. Trans. Vol. 2 Page 40 no. 1885).

To proceed: The religion of Islam is that which has been ordained by Allah, fully explained by the prophet sallallahu alaihiwasallam as understood and practised by the salaf-us-saliheen (the pious predecessors which includes the Sahabah, Tabi'een and their followers).

 The Sunnah has been preserved in its pristine purity in the books of Sunnah only because of the chain of narrators (isnaad) reaching up to the Prophet sallallahu alaihiwasallam, has been meticulously preserved by the Muhadditheen (Scholars of Hadeeth). In the words of Abdullah Ibn al-Mubarak (died 181 A.H.) one of the very illustrious teachers of Imam al-Bukhari, who said.

"The isnaad is part of the religion and had it not been for the isnaad, whoever wished would have said whatever he liked"

Reported by Imam Muslim in the introduction to his Sahih. (Sharh Sahih Muslim - Arabic Vol. 1 Page 87 published by Darul Kuthubul-Islamiyyah, Lebanon).

 Only the narrations which reach the level of Saheeh (authentic) or Hasan (good) as defined by the Scholars (Muhadditheen) are suitable to be held as evidence in matter of belief [such as creed (Aqeedah) and the unseen (ghaib)], in the rulings and laws of the religion or in matters of worship. Only these can be attributed definitely and directly to the Prophet sallallahu alaihiwasallam.

 Narrations which fail to reach these two standards will be collectively termed weak (Da'eef) and should not be attributed directly to the Prophet sallallahu alaihiwasallam in a definite form as clearly explained by Imam Nawawi in Sharh Sahih Muslim (Arabic Vol. 1, Page 81 - Darul Kuthubul Islamiyyah). Weak narrations provided their weakness is not severe, (i.e. There are no liars and / or fabricators and none suspected of lying or fabricating in the chain) can only be used to exhort or warn of a deed (amal) already sanctioned by the other authentic ahaadeeth (singular - hadeeth). If the weakness is severe (as in the case of false, fabricated, etc. ahaadeeth) it cannot be used for the above purpose as well. If such hadeeth are over to be quoted it should be only for the purpose of warning the Muslim community of false and fabricated ahaadeeth. Even then the defect should be clearly stated so that the ahaadeeth will not be attributed to the Prophet sallallahu alaihiwasallam.

 The Muhadditheen have collected such narrations for the purpose of warning the community, in separate books Few examples of such books are :

1. Ak-Maudhooaathul Kubra by Mulla Ali Qari.

2. Al-Maudhooaathul Sughra by Mulla Ali Qari.

3. Al-La'aali-ul-Masnuah fil Ahaadeethil Maudhoo'ah by Imaam Suyooti.

4. Thanzeehus Shareeathil Marfoo'ah anil Ahaadithish- Shaneeathul Maudoo'ah by Ibnul Iraq al-Kan'ani.

 Attributing a saying not told by the Prophet sallallahu alaihiwasallam to the Prophet is a very grave sin and will lead the person to Hell. It is reported from a large number of Sahabah from the Prophet sallallahu alaihiwasallam that he said
  "Whoever lies on me intentionally then let him reserve his seat in hell."

(Sahih Bukhari. Eng. Trans. Book of Knowledge, Chapter - The sin of a person who tells a lie against the Prophet sallallahu alaihiwasallam Vol. 1 Hadeeth no 106 and also by Imam Muslim in his preface to Sahih Muslim).

Also it will include a person among the liars as can be seen in the following two ahaadeeth also found in the preface to Sahih Muslim.

1. "Whoever narrated a hadeeth from me which is seen as a lie then he is one of the liars" [From Sharh Sahih Muslim (Arabic) by Imam Nawawi Vol. 1 Page 62 - Darul Kuthubul Islamiyyah]

2. "It is sufficient for a person to be a liar that he narrates all that he hears" (page 73 of the book referred to above).

 And commenting on the above Imam Nawawi goes on to say "....... and there is no difference in the prohibition of lying on the Prophet either in what concerns the laws of the religion or in other than the laws like exhorting, warning, advising and the like of it, all of this is Haram (Forbidden). It is from the greatest of the grave sins and vilest of the abominable matters in the unanimous opinion of the Muslims ..etc"