Musnad Ahmad 33:723

Yunus, Surayj, and ‘Affan narrated to us, they said: Hammad narrated to us—‘Affan said in his narration: Abu al-Zubayr informed us, from Jabir, who said: "We slaughtered horses, mules, and donkeys on the day of Khaybar. The Messenger of Allah (peace and blessings of Allah be upon him) forbade us from the mules and the donkeys, but he did not forbid us from the horses."