Sahih Muslim Book 27, Hadith 54
" There fell from my hand the whip on account of his (the Prophet's) awe."
I was beating my slave with a whip when I heard a voice behind me: Understand, Abu Masud; but I did not recognise the voice due to intense anger. He (Abu Mas'ud) reported: As he came near me (I found) that he was the Messenger of Allah (ﷺ) and he was saying: Bear in mind, Abu Mas'ud; bear in mind. Abu Mas'ud. He (Aba Maslad) said: threw the whip from my hand. Thereupon he (the Holy Prophet) said: Bear in mind, Abu Mas'ud; verily Allah has more dominance upon you than you have upon your slave. I (then) said: I would never beat my servant in future.
When I was beating my servant, I heard a voice behind me (saying): Abu Mas'ud, bear in mind Allah has more dominance over you than you have upon him. I turned and (found him) to be Allah's Messenger (ﷺ). I said: Allah's Messenger, I set him free for the sake of Allah. Thereupon he said: Had you not done that, (the gates of) Hell would have opened for you, or the fire would have burnt you.