Musannaf Ibn Abi Shayba 19:313

Abu Bakr narrated to us, he said: Abu Mu'awiyah narrated to us, from al-A'mash, from Ibrahim, from Hammam, from 'Amr ibn Sharhabil, he said: Ma'qil al-Muzani came to 'Abdullah and said: "My slave girl has committed adultery." He said: "Flog her fifty [times]."