The Book Pertaining to the Merits of the Companions (Allah Be Pleased With Them) of the Holy Prophet (May Peace Be Upon Him) (Kitab Al-Fada'il Al-Sahabah)
Muslim :: Book 31 : Hadith 6088
'Ali reported that Allah's Messenger (may peace be upon him) sent me and Abu Marthad al-Ghitnavi and Zubair b. 'Awwam and we were all riders, and he said: Ride on until you reach the garden of Khakh for there is a woman amongst the polytheists and there is a letter with her sent by Hatib to the polytheists; the rest of the hadith is the same.