Sahih Muslim Book 021, Hadith Number 4768.
Chapter : The eating of the flesh of domestic asses is unlawful.
Shaibani reported: I asked 'Abdullah b. Abu Aufa about (the lawfulness or unlawfulness of) the flesh of the domestic asses. He said: We experienced hunger on the Day of Khaibar as we were with the Messenger of Allah (may peace be upon him). We found domestic asses in the exterior of Medina. We slaughtered them and our earthen pots were boiling when the announcer of the Messenger of Allah (may peace be upon him) made an announcement that the earthen pots should be turned upside down and nothing of the flesh of the domestic asses should be eaten. I said: What kind of prohibition is it that he (the Holy Prophet) has made? He said: We discussed it amongst -ourselves. Some of us aaid that it has been declared unlawful for ever, (whereas others said) it has been declared unlawful since one-fifth (of the booty) has not been given (to the treasury, as is legally required).