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: 4777
Anas reported: When Allah's Messenger (may peace be upon him) conquered Khaibar, we caught hold of the asses outside the village. We cooked them (their flesh). Then the announcer of Allah's Messenger (may peace be upon him) made the announcement: Listen, verily Allah and His Messenger have prohibited you (the eating of) their (flesh), for it is a loathsome evil of Satan's doing. Then the earthen pots were turned over along with what was in them, and these were brimming (with flesh) at that time.