Imaam Al-Qurtubee said in his famous tafseer:
“His statement “their women” refers to the Muslim women (1). The polytheist women, such as the disbelievers and their types are exempt from this. It is not permissible for a believing woman to uncover any part of her body in the presence of a disbelieving woman, unless she is her slave/servant.
Some scholars considered it detestable for a Muslim woman to host a Christian woman or have her ‘awrah looked at by her.
‘Umar Ibn Al-Khattaab once wrote a letter to Aboo ‘Ubaydah Ibn Al-Jarraah saying:
‘It has reached me that the Muslim women enter the public wash areas along with the disbelieving women. So prevent this and do not allow it, for indeed it is not permissible for a disbelieving woman to see a Muslim woman uncovered.’
So Aboo ‘Ubaydah stood up at that and called out saying:
‘Whichever woman enters the public bath areas without an excuse, not wanting except to purify her face, then may Allaah darken her face on the day when the faces will be whitened (purified).’ “
[Tafseer Al-Qurtubee, 12/233]
(1) This is based on the saying of Allaah: “…And (tell them) not to reveal their zeenah (adornment) except to their husbands, their fathers… their women…” [Soorah Noor: 30-31]
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]