Maliks Muwatta Book 9, Hadith Number 30.
Section : The Prayer of Duha.
Yahya related to me from Malik from Musa ibn Maysara from Abu Murra, the mawla of Aqil ibn Abi Talib, that Umm Hani bint Abi Talib told him that in the year of the conquest the Messenger of Allah, may Allah bless him and grant him peace, prayed eight rakas, covering himself with one garment.