Praise be to Allah.
It is prescribed for a woman to leave her face uncovered during Hajj and ‘umrah, unless she is afraid that men will see her, in which case it is obligatory for her to cover it, but without using the niqab or burqa‘ [types of face veils] and the like, which are tailored to fit the size of the face, because of the report narrated by Abu Dawood (1833) from ‘Aa’ishah, who said: The riders would pass by us while we were with the Messenger of Allah (blessings and peace of Allah be upon him) in the state of ihram. When they were next to us, one of us would lower her jilbab from her head over her face, then when they had passed, she would uncover it.
Classed as da‘eef by al-Albaani in al-Irwa’ (1024)
Al-Haafiz (may Allah have mercy on him) said:
Ibn Abi Khaythamah narrated via Ismaa‘eel ibn Abi Khaalid from his mother, who said: We used to enter upon the Mother of the Believers on the day of at-Tarwiyah (8th Dhu’l-Hijjah). I said to her: O Mother of the believers, here is a woman who refuses to cover her face and she is in ihram. ‘Aa’ishah lifted her khimaar from her chest and covered her face with it.
End quote from at-Talkhees al-Habeer (2/576)
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked:
What is the ruling on a woman wearing a burqa‘ or lithaam (types of face veils) when in the state of ihram?
As for the burqa‘, the Prophet (blessings and peace of Allah be upon him) forbade a woman to wear niqab when in ihram, and that applies even more so to the burqa‘. Based on that, she may cover her face completely with her khimaar (head cover), if there are non-mahram men around her. If there are no non-mahram men around her, then she may uncover her face. This is best and is Sunnah.
End quote from Majmoo‘ Fataawa wa Rasaa’il ash-Shaykh (22/186)
Based on that:
However a woman covers her face, that is permissible, on condition that it is not done with the niqab and similar covers that are tailored to the size of the face.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
The fact that the niqab is singled out for being disallowed, along with the gloves, indicates that he only forbade that which is made to cover the face, like the gloves which are made to cover the hands, and the chemise is made to cover the body. Based on that, it is permissible to cover it with one’s garment, from beneath or from above, so long as it is not made in a manner to fit the face, and she may cover it with a blanket when sleeping.
End quote from Sharh al-‘Umdah (3/270)
Shaykh Saalih al-Fawzaan (may Allah preserve him) said:
Women are only prohibited to wear the burqa‘ and niqab (face veils) made of made and tailored especially for the face.
End quote from al-Muntaqa min Fataawa al-Fawzaan (52/11)
And Allah knows best.