Musnad Ahmad 5:572

Abdullah narrated to us, Abu Bakr ibn Abi Shaybah narrated to me, Waki' narrated to us, and Sufyan ibn Waki' narrated to us, my father narrated to us, from Abu Janab, from Abu Jamilah al-Tahawi, he said: I heard Ali saying: The Messenger of Allah, peace and blessings of Allah be upon him, was cupped. Then he said to the cupper when he finished: "What is your fee?" He said: "Two sa's." So he remitted one sa' for him, and he commanded me, so I gave him one sa'.