I have caused you pain. He said: No. But he (Ibn Umar) said: You are free. He then took hold of something from the earth and said: There is no reward for me even to the weight equal to it. I heard Messenger of Allah ﷺ as saying: He who beats a slave without cognizable offence of his or slaps him (without any serious fault), then expiation for it is that he should set him free.  

مَا لِي فِيهِ مِنَ الأَجْرِ مَا يَزِنُ هَذَا إِنِّي سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ مَنْ ضَرَبَ غُلاَمًا لَهُ حَدًّا لَمْ يَأْتِهِ أَوْ لَطَمَهُ فَإِنَّ كَفَّارَتَهُ أَنْ يُعْتِقَهُ  

I came to Ibn ‘Umar when he set his slave free. He took a stick or something else from the earth and said; for me there is no reward even equivalent to this. I heard the Messenger of Allah (May peace be upon him) say: If anyone slaps or beats his slave the atonement due from him is to set him free.  

مَا لِي فِيهِ مِنَ الأَجْرِ مَا يَسْوَى هَذَا سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ مَنْ لَطَمَ مَمْلُوكَهُ أَوْ ضَرَبَهُ فَكَفَّارَتُهُ أَنْ يُعْتِقَهُ  

[Machine] I heard the Messenger of Allah ﷺ saying, "Whosoever strikes his servant, causing them pain or slaps them, their expiation is to set them free."  

سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ مَنْ ضَرَبَ غُلَامًا لَهُ حَدًّا لَمْ يَأْتِهِ أَوْ لَطَمَهُ فَإِنَّ كَفَّارَتَهُ أَنْ يُعْتِقَهُ