Musannaf Ibn Abi Shayba 19:292

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from ‘Uyaynah ibn ‘Abd al-Rahman, from his father: That when ‘Umar ordered Abu Bakrah and his companions, they were flogged. Then Abu Bakrah returned and said: "Al-Mughirah committed adultery." ‘Umar wanted to flog him, but ‘Ali said: "For what are you flogging him? Did he say anything other than what he had already said?" So he left him.