Musnad Ahmad 5:804

Muhammad ibn Ubayd narrated to us, Muhammad ibn Ishaq narrated to us, from Abdullah ibn Abi Najih, from Mujahid, from Abd al-Rahman ibn Abi Layla, from Ali, may Allah be pleased with him, who said: When the Messenger of Allah, peace and blessings of Allah be upon him, slaughtered his sacrificial camels, he slaughtered thirty with his own hand, and he commanded me, so I slaughtered the remainder of them. He said: "Distribute their meat among the people, and their hides and their coverings, and do not give the butcher anything from them."