Sahih Muslim
The Book of Games and the Animals which May be Slaughtered and the Aninals that Are to be Eaten (Kitab-us-Said wal-Dhabaih wa ma Yukalu min Al-Hayawan)
Book Number: 021 / Hadith Number: 4780
Jabir b. 'Abdullah is reported to have said: We ate during the time of Khaibar the (flesh) of horses and of wild asses, but Allah's Messenger (may peace be upon him) prohibited us (to eat) the flesh of domestic asses. This hadith has hen transmitted on the authority of Ibn Juraij.