(93) بَابُ مَنْ لَطَمَ عَبْدَهُ فَلْيُعْتِقْهُ مِنْ غَيْرِ إِيجَابٍ
Abu 'Umar Zadhan said, "We were with Ibn 'Umar when he summoneda slave of his whom he had beaten and he uncovered his back. 'Does it hurt?'he asked. 'No,' he replied. Then he set him free. He picked up a stickfrom the ground and then said, 'I do not have a reward (for him) worthas much as this stick.' I asked, 'Abu 'Abdu'r-Rahman, why do you say this?'He replied, 'I heard the Prophet, may Allah bless him and grant him peace,say, "The expiation of someone who beats a slave more than he deservesor slaps his face is that he must set him free."'"
Reference: Al-Adab Al-Mufrad 180
In-book reference: Book 9, Hadith 25
English translation: Book 9, Hadith 180