Musnad Ahmad 5:438

Yahya narrated to us, Ibn Jurayj narrated to us, Hassan ibn Muslim and Abd al-Karim informed me that Mujahid informed them both that Abd al-Rahman ibn Abi Layla informed him that Ali informed him: "That the Prophet, peace and blessings of Allah be upon him, commanded him to stand over his sacrificial animals (budn), and commanded him to distribute all of their meat, their skins, and their coverings, and not to give anything from them as payment for their slaughtering."