Bear in mind, O Abu Mas‘ūd, that Allah has more power over you than you have over this boy. I said: I will never beat a slave ever again

Abu Mas‘ūd (may Allah be pleased with him) was beating his slave boy with a whip. He heard a voice from behind rebuking him but he could not identify the speaker. When the speaker came near to him, he recognized that it was the voice of the Messenger of Allah (may Allah's peace and blessings be upon him) reminding him of the power of Allah, the Almighty, by saying: "Bear in mind, Abu Mas‘ūd, that Allah has more power over you than you have over this boy."

So when he heard what the Prophet (may Allah's peace and blessings be upon him) said and his warning against abusing the weak, the whip fell from his hand in awe of the Messenger of Allah, and he promised him that he would never abuse any slave after that. Also, after he heard the Prophet's rebuke and warning, he immediately set the slave free to expiate for beating him.

Thereupon, the Prophet (may Allah's peace and blessings be upon him) said: "If you had not freed him, the fire would have afflicted you on the Day of Resurrection because of the evilness of your deed."