You could find no other part (to slap) but the prominent part of her face. See I was one of the seven sons of Muqarrin, and we had but only one slave-girl. The youngest of us slapped her, and Allah's Messenger (ﷺ) commanded us to set her free. 2097
Sahih Muslim Book 27, Hadith 49
← Previous Hadith I slapped a slave belonging to us and then fled away. I came back just before noon and offered prayer behind my father. He called him (the slave) and me and said: Do as he has done to you. He granted pardon. He (my father) then said: We belonged to the family of Muqarrin during the lifetime of Allah's Messenger (may peace be upon him. and had only one slave-girl and one of us slapped her. This news reached Allah's Apostle (ﷺ) and he said: Set her free. They (the members of the family) said: There is no other servant except she. Thereupon he said: Then employ her and when you can afford to dispense with her services, then set her free.

Sahih Muslim Book 27, Hadith 48 Next Hadith → We used to sell cloth in the house of Suwaid b. Muqarrin, the brother of Nu'man b. Muqarrin. There came out a slave-girl, and she said something to a person amongst us, and he slapped her. Suwaid was enraged-the rest of the hadlth is the same.

Sahih Muslim Book 27, Hadith 50