Musnad Ahmad 433:3

Yazid ibn Abd Rabbih narrated to us, Baqiyyah ibn al-Walid narrated to us, Thawr ibn Yazid narrated to me, from Salih ibn Yahya ibn al-Miqdam ibn Ma'di Karib, from his father, from his grandfather, from Khalid ibn al-Walid, who said: "The Messenger of Allah, may Allah bless him and grant him peace, forbade the eating of the meat of horses, mules, and donkeys."