Sayyidina Abu. (RA) narrated I was beating my slave. Suddenly, I heard a speaker behind me say, “Beware, O Abu Mas’ud! Beware, O Abu Mas’ud!” So, I turned (my face) and as I was facing Allah’s Messenger (SAW). He said, “Allah is more powerful over you than you are over him.” After that, I never beat a servant.
[Muslim 1659]