Refutation For those who claim niqaab is not wajib and the face and hands of a woman can be seen by (ghairMahrrum) strange men.

Refutation from Shaikh Ibn Uthaymeen This is taken from the book "Hijaab" by Shaikh Ibn Uthaymeen from Saudi Arabia.  Printed by Madrasah Arabia Islamia Azaadville- South Africa.
Translated by Hafedh Zaheer Essack, Rajab 1416 (December 1995)

The Ulamah who are of the opinion that it is permissible to look at the face and hands of a strange woman (who is not mahrrum) say so mainly for the following reasons.

The hadeeth of Ayeshah (Radhiallaahu Ánha) when Asmaa (Radhiallaahu Ánha) the daughter of Abu Bakr came to the Rasulullaah (Sallallaahu Álayhi Wasallam) while wearing thin clothing. He approached her and said: 'O Asmaa! When a girl reaches the menstrual age, it is not proper that anything should remain exposed except this and this. He pointed to the face and hands. But this hadeeth is WEAK because of 2 main weaknesses.
1. There is no link between Ayeshah (Radhiallaahu Ánha) and Khalid bin Dareek, who narrated the hadith from her. And  in every chain of narrators Khalid bin Dareek is mentioned.
2.  In the chain of narrators Sa'eed bin Basheer appears, who is known by most of the Muhaditheen as being a weak narrator.  

This has been mentioned by Imaam Ahmad bin Hanbal (Rahimahullah), An-Nasai (Rahimahullah), Ibn Madeeni (Rahimahullah) and Ibn Ma'een (Rahimahullah).  This is also why Imaam Bukhari (Rahimahullah) and Muslim (Rahimahullah) did not except this hadeeth to be in their books. (From Shaikh Ibn Uthaymeen in the book "Hijaab" pages # 17 and 18.)

We also have to see that the Muhadith Abu Dawood when he quoted this hadeeth put with it that it is Mursal (with a broken chain that does not lead up to the Sahabah).
(From The Book "Hijaab wa Safur" under the fatwaa of Shaikh Abdul Aziz Bin Bazz on Page #61. Also stated as being weak by Shaikh Nasiruddeen Al-Albaani in his Daeef Sunan Abu Dawud in Kitab-ul-Libas under hadeeth number 4092 (which is the original hadeeth number.) It has also been mentioned in the magazine called "Al Hijrah" that Ulama agree this hadeeth is weak.)

An other thing that shows the weakness of this hadith is that after the ayah for hijab (Surah Al-Ahzaab – Verse #59) was revealed then the women of Sahaba wore a complete veil and covered the faces and hands.  This includes Asmaa (Radhiallaahu Ánha) the daughter of Abu Bakr, who is supposed to have narrated this hadeeth.  Asmaa (Radhiallaahu Ánha) covered herself completely including the face, this has been narrated in authentic hadeeth in Imaam Malik's "MUWATTA Book 20 Hadeeth # 20.5.16."