Musnad Ahmad 32:792

Muhammad ibn Ja'far narrated to us, Sa'id narrated to us, from Qatadah, from Anas ibn Malik, that the Messenger of Allah (peace and blessings of Allah be upon him) saw a man driving a sacrificial camel. He said, "Ride it." The man said, "It is a sacrificial camel." He said, "Ride it." The man said, "It is a sacrificial camel?" He said, "Ride it."