Sayyiduna Anas bin Malik (may Allah be pleased with him) said that on the day of Khaybar, a companion stood up and said: "O Messenger of Allah! The donkeys have been eaten," or he said: "The donkeys have been finished (by eating them)." Then he said: "O Messenger of Allah! The donkeys have been finished," or "have been eaten." Thereupon, the Messenger of Allah (peace and blessings be upon him) ordered a companion to announce: "Indeed, Allah and His Messenger both forbid you from eating the meat of domesticated donkeys because they are impure."
Hadith Referenceسنن دارمي / من كتاب الاضاحي / 2030