Musannaf Ibn Abi Shayba 19:483

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from Ma’mar, from al-Zuhri, that Marwan flogged both of them forty [lashes] each and separated them. Qabisah ibn Dhu’ayb said to him, "If you had lightened it and flogged them twenty [lashes] each."