Musnad Ahmad 32:277

Yazid narrated to us, Hisham informed us, from Muhammad ibn Sirin, from Anas ibn Malik, who said: The Messenger of Allah (may Allah bless him and grant him peace) commanded Abu Talhah during the Battle of Khaybar to proclaim: "Indeed, Allah and His Messenger forbid you from the meat of domestic donkeys, for it is an abomination." He said: So the cooking pots were overturned.