Some scholars claim that the niqaab (face veil) is not an obligation, using as evidence the following narration:
“Asmaa Bint Abee Bakr entered in the presence of Allaah’s Messenger whilst wearing a thin, transparent garment. So the Messenger of Allaah turned away from her saying: “O Asmaa Indeed when a woman reaches the age of puberty, it is not allowed that any of her be seen except for this and this.” And he pointed to his face and hands.” [Aboo Daawood]
Ibn ‘Uthaymeen refutes this claim and says about this hadeeth:
“As for the hadeeth of ‘Aa’ishah, then it is da’eef (weak) based on two aspects:
1) The break in the chain between ‘Aa’ishah and Khaalid Bin Duraik, which was reported by Aboo Daawood, who noted the deficiency himself when he stated that Khaalid Bin Duraik never heard from ‘Aa’ishah. Aboo Haatim Ar-Raazee, may Allaah have mercy upon him, also mentioned this weakness.
2) One of the narrators in its chain is Sa’eed Bin Basheer An-Nasree, a settler in damascus, who was renounced by Ibn Mahdee and declared weak by Imaam Ahmad, Ibn Ma’een, Ibn Madeenee, and An-Nisaa’ee. Due to this, the hadeeth is da’eef and cannot be used as an argument against the authentic hadeeths mentioned previously, which prove the obligation of veiling (of the face and hands).
3) Furthermore, Asmaa Bint Abee Bakr was 27 years old when the Prophet made Hijrah. So being that she was mature and advanced in age, it would be unthinkable to suspect that she would enter the presence of the Prophet (saw) with a thin and tight dress, such that it revealed from her, more than just her hands and face. And Allaah knows best.
4) And even if we were to assume that this hadeeth was authentic, it probably took place before te advent of Hijaab. This is since the texts concerning teh hijaab can be traced back to the original state, so they take precedence.”
[Taken from “The Four Essays On The Obligation Of Veiling”, Pp. 49-50]