حَدَّثَنِي أَبُو كَامِلٍ، فُضَيْلُ بْنُ حُسَيْنٍ الْجَحْدَرِيُّ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ فِرَاسٍ، عَنْ ذَكْوَانَ أَبِي صَالِحٍ، عَنْ زَاذَانَ أَبِي عُمَرَ، قَالَ أَتَيْتُ ابْنَ عُمَرَ وَقَدْ أَعْتَقَ مَمْلُوكًا - قَالَ - فَأَخَذَ مِنَ الأَرْضِ عُودًا أَوْ شَيْئًا فَقَالَ مَا فِيهِ مِنَ الأَجْرِ مَا يَسْوَى هَذَا إِلاَّ أَنِّي سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ ‏"‏ مَنْ لَطَمَ مَمْلُوكَهُ أَوْ ضَرَبَهُ فَكَفَّارَتُهُ أَنْ يُعْتِقَهُ ‏"‏.
Translation
Zadhan reported that Ibn Umar called his slave and he found the marks (of beating) upon his back. He said to him

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 Allah's Messenger (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.