Hadith 503250
Chapter 8: Prayer in Congregation - كتاب صلاة الجماعة
حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَائِشَةَ، زَوْجَ النَّبِيِّ صلى الله عليه وسلم كَانَتْ تُصَلِّي فِي الدِّرْعِ وَالْخِمَارِ .
Yahya related to me from Malik that he had heard that A'isha, the wife of the Prophet, may Allah bless him and grant him peace, used to pray in a shift and head-covering.
Reference Muwatta Malik 503250
USC-MSA web (English) reference : Book 8, Hadith 36