Sahih Muslim Book 15, Hadith Number 4083.

Chapter : How should the masters treat their slaves and expiation if they show high-handedness.

Hilal b. Yasaf reported: 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 hadith is the same.