Musannaf Ibn Abi Shayba 19:205

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, so shall I flog her?" He said: 'Abdullah said: "Flog her fifty." He said: "She did it again." He said: "Flog her."