Musnad Ahmad 1087:1

Abdullah ibn Idris narrated to us, from Muhammad ibn Ishaq, from Muhammad ibn Amr ibn Ata, from Sulayman ibn Yasar, from Salamah ibn Sakhr al-Bayadi, who said: I was a man who would obtain from women what others would not obtain. He said: When the month of Ramadan entered, I feared, so I performed *zihar* (declaring my wife like my mother's back) upon my wife for the month. He said: While she was serving me one night, something of her was revealed to me, and I did not delay before I fell upon her. So I came to the Messenger of Allah, peace and blessings of Allah be upon him, and informed him. He said: "Free a slave." I said: By the One who sent you with the truth, I do not possess a slave other than my own neck. He said: "Then fast two consecutive months." I said: And did what afflicted me afflict me except because of fasting? He said: "Then feed sixty poor people."