Sahih Muslim Book 27, Hadith 51
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.
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.
Shu'ba informed that Muhammad b. Munkadir said to me: What is your name? The rest of the hadith is the same.