Musnad Ahmad 5:718

'Abdullah narrated to us, 'Uthman ibn Abi Shaybah narrated to me, Sharik narrated to us, from Abu al-Hasna', from al-Hakam, from Hanash, who said: I saw 'Ali, may Allah be pleased with him, sacrificing two rams. I said to him: "What is this?" He said: "The Messenger of Allah, may Allah bless him and grant him peace, instructed me to sacrifice on his behalf."