Full Sharh — Sahih Muslim 4298
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 "
English Translation
Zadhan Abl Umar reported:I came to Ibn 'Umar as he had granted freedom to a stave. He (the narrator further) said: He took hold of a wood or something like it from the earth and said: It (freedom of a slave) has not the reward evert equal to it, but the fact that I heard Allah's Messenger (way peace be upon him) say: He who slaps his slave or beats him, the expiation for it is that he should set him free
Source
Sahih Muslim(صحيح مسلم)
The Book of Oaths
Hadith Number
4298