Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) says: At the time of Khaybar we ate the meat of horses and wild donkeys, and the Prophet (peace and blessings be upon him) forbade eating the meat of the domestic donkey.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19406