Abu Mas'ud [Al-Ansari] said:"I was beating a slave of mine and I heard someone behind me saying: 'Beware O Abu Mas'ud! Beware O Abu Mas'ud!' So I turned around and saw that it was the Messenger of Allah. He said: 'Allah has more power over you than you do over him." Abu Mas'ud said: "I have not beaten any slave of mine since then

English translation · Jami' at-Tirmidhi