كتاب الأيمان
27  
The Book of Oaths
(8)
Chapter: Treatment of slaves, and the expiation of one who slaps his slave
(8)
باب صُحْبَةِ الْمَمَالِيكِ وَكَفَّارَةِ مَنْ لَطَمَ عَبْدَهُ ‏‏
Sahih Muslim 1658 d

Suwaid b. Muqarrin reported that he had a slave-girl and a person (one of the members of the family) slapped her, whereupon Suwaid said to him:

Don't you know that it is forbidden (to strike the) face. He said: You see I was the seventh one amongst my brothers during the lifetime of Allah's Messenger (ﷺ), and we had but only one servant. One of us got enraged and slapped him. Thereupon Allah's Messenger (ﷺ) commanded us to set him free.
وَحَدَّثَنَا عَبْدُ الْوَارِثِ بْنُ عَبْدِ الصَّمَدِ، حَدَّثَنِي أَبِي، حَدَّثَنَا شُعْبَةُ، قَالَ قَالَ لِي مُحَمَّدُ بْنُ الْمُنْكَدِرِ مَا اسْمُكَ قُلْتُ شُعْبَةُ ‏.‏ فَقَالَ مُحَمَّدٌ حَدَّثَنِي أَبُو شُعْبَةَ الْعِرَاقِيُّ عَنْ سُوَيْدِ بْنِ مُقَرِّنٍ أَنَّ جَارِيَةً لَهُ لَطَمَهَا إِنْسَانٌ فَقَالَ لَهُ سُوَيْدٌ أَمَا عَلِمْتَ أَنَّ الصُّورَةَ مُحَرَّمَةٌ فَقَالَ لَقَدْ رَأَيْتُنِي وَإِنِّي لَسَابِعُ إِخْوَةٍ لِي مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم وَمَا لَنَا خَادِمٌ غَيْرُ وَاحِدٍ فَعَمَدَ أَحَدُنَا فَلَطَمَهُ فَأَمَرَنَا رَسُولُ اللَّهِ صلى الله عليه وسلم أَنْ نُعْتِقَهُ ‏.‏
Reference : Sahih Muslim 1658d
In-book reference : Book 27, Hadith 51
USC-MSA web (English) reference : Book 15, Hadith 4084
  (deprecated numbering scheme)