Chapter 28: The Book of Oaths
Abu Mas' ud reported that he had been beating his slave and he had been saying: I seek refuge with Allah, but he continued beating him, whereupon he said: I seek refuge with Allah' s Messenger, and he spared him. Thereupon Allah' s Messenger (ﷺ) said: By Allah, God has more dominance over you than you have over him (the slave). He said that he set him free.
Sahih Muslim 1659d