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 4766
Ibn Umar reported that Allah's Messenger (way peace be upon him) forbade the eating of the flesh of domestic asses.