Musnad Ahmad 32:100

Ibn Abi ‘Adi narrated to us, from Humayd, from Thabit, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) saw a man driving a sacrificial camel that had been exhausted by walking. He said: "Ride it." The man said: "O Messenger of Allah, it is a sacrificial camel." He said: "Ride it, even if it is a sacrificial camel."