Musnad Ahmad 299:7

Ishaq ibn Isa narrated to us, he said: Malik narrated to us, from Yazid ibn Khusayfah, that Amr ibn Abdullah ibn Ka’b informed him, from Nafi’ ibn Jubayr, from Uthman ibn Abi al-As, who said: The Messenger of Allah, peace and blessings of Allah be upon him, came to me while I had a pain that had almost destroyed me. The Messenger of Allah, peace and blessings of Allah be upon him, said to me: "Wipe it with your right hand seven times, and say: 'I seek refuge in the might of Allah and His power from the evil of what I feel.'" He said: So I did that, and Allah took away what I had, and I have not ceased to command my family and others to do it.