Musnad Ahmad 327:1

'Abd al-Salam ibn Harb al-Mula'i narrated to us, from Ishaq ibn 'Abd Allah ibn Abi Farwah, from Bukayr ibn 'Abd Allah ibn al-Ashajj, from Sulayman ibn Yasar, from Salamah ibn Sakhr al-Zurqi, who said: "I performed *zihar* (declaring my wife unlawful to me like my mother) upon my wife, then I had intercourse with her before I had offered the expiation. So I asked the Prophet, peace and blessings of Allah be upon him, and he gave me a legal ruling regarding the expiation."