Musannaf Ibn Abi Shayba 19:264

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Abu Bishr, from Abu Rawh, that a woman resembled a slave-girl belonging to a man, and that was at night. He had intercourse with her while thinking that she was his slave-girl. He said: So that was raised to Umar. He said: So he sent for Ali and said: "Inflict the prescribed punishment (hadd) upon the man in private, and inflict the prescribed punishment (hadd) upon the woman in public."