Exodus 32:25-29

Now when Moses saw that the people were out of control—for Aaron had let them get out of control to be a derision among their enemies— then Moses stood in the gate of the camp, and said, “Whoever is for the LORD, come to me!” And all the sons of Levi gathered together to him. He said to them, “Thus says the LORD, the God of Israel, ‘Every man of you put his sword upon his thigh, and go back and forth from gate to gate in the camp, and kill every man his brother, and every man his friend, and every man his neighbor.’ ” So the sons of Levi did as Moses instructed, and about three thousand men of the people fell that day. Then Moses said, “Dedicate yourselves today to the LORD—for every man has been against his son and against his brother—in order that He may bestow a blessing upon you today.”