Is it permissible for a person in a state of ihram (ritual consecration) for Hajj to cover his feet while sleeping due to coldness? Please advise. May Allaah bless you!

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

It is permissible for a man in the state of ihram for Hajj or ‘Umrah to cover his feet with his upper or lower Hajj garment, etc.  But he should not wear form-fitting clothes, such as socks, on any part of his body. The Prophet, sallallaahu ‘alayhi wa sallam, said, "You should not wear shirts, turbans, hooded cloaks, trousers, or khuff (leather socks) except when one does not find sandals; he may [then] put on leather socks, but he should trim them to be below the ankles." [Al-Bukhari and Muslim]

Explaining the Hadeeth, An-Nawawi said:

By mentioning 'leather socks', the Prophet, sallallaahu ‘alayhi wa sallam, forbade wearing any type of footwear that covers the foot entirely, such as shoes, jumjum, and socks, etc which cover the feet. This ruling is specific to men. Women, on the contrary, are allowed to cover the whole body with form-fitting clothes and other clothes as well, except for the face.

Allaah Knows best.