Someone who slaps his slave should free him even Al-Adab Al-Mufrad 177
Arabic hadith text
حَدَّثَنَا عَمْرُو بْنُ عَوْنٍ، وَمُسَدَّدٌ، قَالاَ: حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ فِرَاسٍ، عَنْ أَبِي صَالِحٍ، عَنْ زَاذَانَ، عَنِ ابْنِ عُمَرَ قَالَ: سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ: مَنْ لَطَمَ عَبْدَهُ أَوْ ضَرَبَهُ حَدًّا لَمْ يَأْتِهِ، فَكَفَّارَتُهُ عِتْقُهُ.
Translation
Ibn 'Umar said, "I heard the Prophet, may Allah bless him and grant him peace, say, 'The expiation for someone who slaps his slave or beats him more than he deserves is to set him free.'"