Musannaf Ibn Abi Shayba 3:3794

Waki' narrated to us, he said: Malik ibn Anas narrated to us, from Bukayr ibn 'Abdullah ibn al-Ashajj, from 'Ubaydullah al-Khawlani, from Maymunah bint al-Harith, the wife of the Prophet, may Allah bless him and grant him peace: That she prayed in a chemise (dir') and a head covering (khimar).