The Book of Games and the Animals which May be Slaughtered and the Aninals that Are to be Eaten (Kitab-us-Said wa'l-Dhaba'ih wa ma Yu'kalu min Al-Hayawan)
Muslim :: Book 21 : Hadith 4779
Jabir b. 'Abdullah reported that Allah's Messenger (may peace be upon him) prohibited eating of the flesh of domestic asses on the Day of Khaibar, and permitted the cooking of the flesh of horses.