Musannaf Ibn Abi Shayba 35:284

Abu Khalid al-Ahmar narrated to us, from Humayd, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) saw a man driving a sacrificial camel. He said, "Ride it." The man said, "It is a sacrificial camel." He said, "Ride it."