Musannaf Ibn Abi Shayba 19:773

Abu Bakr narrated to us, he said: Abda bin Sulayman narrated to us, from Sa’id, from Qatada, from Sa’id bin al-Musayyib regarding a man who said to his wife, "I saw you committing adultery before you were with me." Sa’id said: "A prescribed punishment (hadd) is due, and there is no invoking of curses (li’an)." Al-Hasan said: "There is no prescribed punishment and no invoking of curses, because he said that to her while she was with him."