Sahih Muslim Book 15, Hadith Number 4090.

Chapter : It is improper to accuse the slave of adultery.

Abu Huraira reported that Abu’l-Qasim (one of the names of Allah’s Messenger [may peace be upon him]) said: He who accused his slave of adultery, punishment would be imposed upon him on the Day of Resurrection, except in case the accusation was as he had said.