Sayyiduna Abu Mas'ud (may Allah be pleased with him) said: I was beating a slave of mine with a whip when suddenly I heard a voice behind me: "Know, O Abu Mas'ud!" Because of my anger I could not make sense of it, until the Messenger of Allah (peace and blessings be upon him) came close to me. When I saw him (peace and blessings be upon him), the whip fell from my hand. He (peace and blessings be upon him) said: "Know, O Abu Mas'ud, that Allah has far more power over you than you have." I said: "By the One who sent you with the truth, I will never again beat any slave."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14756