Ibn Mas’ood reported that the Messenger of Allaah said: “The woman is ‘awrah.”
This is a clear-cut proof that every part of a woman is ‘awrah (i.e. must be covered) in front of male strangers, whether that includes her face, or any otter part of her body. In fact, her face and hands have the most right to be covered since they are the areas that are sought after by men and the places of enticement from women.
Imaam Ahmad Ibn Hanbal understood well the aforementioned hadeeth of Ibn Mas’ood, as he said:
“A woman’s fingernail is ‘awrah (i.e. it must be covered). So when she goes out from her home, she must not reveal any part of herself, not even her khuff (sock), for the chuff describes the foot. What is preferred, in my opinion, is that she put a button on her sleeve where her hand is so that nothing could be exposed from her.”
Many scholars and Imaams throughout the history of time have come up with the same understanding of the hadeeth of Ibn Mas’ood and other similar texts as that of Imaam Ahmad Ibn Hanbal – that the entire body of a woman is ‘awrah without the exception of the face and hands…
As for the logical proof, then from the things which there is no doubt according to sane and unbiased people is that the fitnah involved in a woman unveiling her face and hands is greater than that of her exposing her feet, foe which the Prophet (saw) ordered the women to lengthen the hems of their dresses by a forearm’s length so that their feet would not be exposed.”
[Taken from “Four Essays On The Obligation Of Veiling” Ch.4: The Obligation Of Veiling The Hands And Face, by Sh. Zayd Ibn Muhammad Ibn Haadee Al-Madkhalee, Pp. 82-83]