It is narrated from Sayyiduna Ammar bin Yasir (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever beats his slave unjustly, retribution will be taken from him on the Day of Resurrection."
Hadith Referenceسلسله احاديث صحيحه / الحدود والمعاملات والاحكام / 1315