A woman who has attained the age of majority is obliged to cover her entire body during prayer, apart from her face and hands, because all other parts are considered ‘awrah. If she prays and any part of her ‘awrah becomes uncovered, such as her shin, foot or a part of her head, then her prayer is invalid. The Prophet said: “Allah will not accept the prayer of a woman who has started to menstruate, except with a khimar (covering)” [Reported by Ahmad, Abu Dawud, Ibn Maajah and al-Tirmidhi, with a sahih isnad].
Abu Dawud reported from Umm Salamah that she asked the Prophet about a woman who prayed wearing a dir’ (chemise or upper garment) and a khimar (head cover), but no izar (lower garment). He said: “The woman is ‘awrah.”
According to the majority of scholars, the feet must be covered; some scholars allow uncovering the feet but the majority say the opposite. Abu Dawud reported from Umm Salamah (may Allah be pleased with her) that she was asked about a woman who prayed in a khimar and qamis (dress or gown). She said, “There is nothing wrong with it if the dir’ (chemise) covers her feet.” In any case, it is better to cover the feet, to be on the safe side.