Muwatta Imam Malik Book of Prayer in Congregation, Hadith 37

Yahya related to me from Malik from Muhammad ibn Zayd ibn Qunfudh that his mother asked Umm Salama, the wife of the Prophet ﷺ "What clothes can a woman wear in prayer?" She said, "She can pray in a shift that reaches down and covers the top of her feet."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ مُحَمَّدِ بْنِ زَيْدِ بْنِ قُنْفُذٍ، عَنْ أُمِّهِ، أَنَّهَا سَأَلَتْ أُمَّ سَلَمَةَ زَوْجَ النَّبِيِّ ﷺ مَاذَا تُصَلِّي فِيهِ الْمَرْأَةُ مِنَ الثِّيَابِ فَقَالَتْ تُصَلِّي فِي الْخِمَارِ وَالدِّرْعِ السَّابِغِ إِذَا غَيَّبَ ظُهُورَ قَدَمَيْهَا .