Exodus 32:25-29

Now when Moses saw that the people were unrestrained (for Aaron had not restrained them, to their shame among their enemies), then Moses stood in the entrance of the camp, and said, “Whoever is on the LORD’s side—come to me!” And all the sons of Levi gathered themselves together to him. And he said to them, “Thus says the LORD God of Israel: ‘Let every man put his sword on his side, and go in and out from entrance to entrance throughout the camp, and let every man kill his brother, every man his companion, and every man his neighbor.’ ” So the sons of Levi did according to the word of Moses. And about three thousand men of the people fell that day. Then Moses said, “Consecrate yourselves today to the LORD, that He may bestow on you a blessing this day, for every man has opposed his son and his brother.”