Musnad Ahmad 32:200

Yahya narrated to us, from Hisham ibn Hassan, Muhammad narrated to us, from Anas, that a man came to the Prophet, may God bless him and grant him peace, at Khaybar and said: "I have eaten donkey meat twice." He said: Then he came and said: "I have finished off the donkeys." He said: "So he called out: 'Indeed, God and His Messenger forbid you from the meat of donkeys, for it is an abomination.'"