Musnad Abu Ya'la al-Mawsili 108:232

Ubayd Allah ibn Umar narrated to us, Hammad narrated to us, Amr narrated to us, from Muhammad ibn Ali, from Jabir ibn Abdullah: That the Messenger of Allah (peace and blessings of Allah be upon him) forbade on the day of Khaybar the meat of domestic donkeys, and he permitted the meat of horses.