Musnad Ahmad 32:19

Hashim narrated to us, he said: And Humayd narrated to us, from Thabit, from Anas—and I think I heard it from Anas—that the Messenger of Allah (peace and blessings of Allah be upon him) passed by a man who was driving a sacrificial camel. He said: "Ride it." The man said: "It is a sacrificial camel." He said: "Ride it," two or three times.