Musannaf Ibn Abi Shayba 3:3793

'Abbad ibn al-'Awwam narrated to us, from Muhammad ibn Ishaq, from Bukayr ibn al-Ashajj, from 'Ubayd Allah al-Khawlani, who said: I saw Maymunah, the wife of the Prophet, may Allah bless him and grant him peace, praying in a single garment (dir'), loosely fitting, and she had placed a portion of its sleeve over her head. He said: And 'Ubayd Allah was an orphan under her care.