Mukhtasar Muslim

Sayyiduna Abu Mas'ud Ansari (may Allah be pleased with him) says: I was beating my slave when suddenly I heard a voice from behind, saying, "Abu Mas'ud! Know that indeed Allah has more power over you than you have over this slave." I turned around and saw that it was the Messenger of Allah (peace and blessings be upon him). I said, "O Messenger of Allah! I have set him free for the sake of Allah (i.e., without any price or condition)." The Prophet (peace and blessings be upon him) said, "If you had not done so, the fire of Hell would have burned you or touched you."

It is narrated from Zadhan that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) called one of his slaves and saw a mark on his back, so he asked, "Did I cause you pain?" He replied, "No." Sayyiduna Ibn Umar (may Allah be pleased with them both) said, "You are free." Then he picked something up from the ground and said, "I did not even receive as much reward as this for freeing him. I heard the Messenger of Allah (peace and blessings be upon him) say: Whoever inflicts a legal punishment on his slave without a reason (i.e., beats him unjustly) or slaps him, its expiation (i.e., compensation, penalty) is that he should set him free."

It is narrated from Sayyiduna Suwaid bin Muqarrin (may Allah be pleased with him) that when a man slapped his slave-girl, Sayyiduna Suwaid (may Allah be pleased with him) said, "Do you not know that hitting the face is forbidden? And look at me: in the blessed time of the Messenger of Allah (peace and blessings of Allah be upon him), we seven brothers had only one servant. One of my brothers slapped her, so the Messenger of Allah (peace and blessings of Allah be upon him) ordered her to be set free."