Musannaf Ibn Abi Shayba 19:770

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from Salih ibn Muslim, from al-Sha’bi, regarding a man who said to a woman: "Bear witness that I have committed adultery with you." He said: "Flog him for what he slandered against her, and do not flog him for what he slandered against himself, except with evidence."