Musnad Ahmad 5:536

Waki’ narrated to us, Saif bin Sulaiman al-Makki narrated to us, from Mujahid, from Ibn Abi Layla, from Ali: "That the Prophet, peace and blessings of Allah be upon him, when he slaughtered the sacrificial camels, commanded me to give away their meat, their hides, and their coverings as charity."