Exodus 32:26-28

26And Moses stood at the camp’s entrance and said, “Whoever is for the Lord, come to me.” And all the Levites gathered around him.

27He told them, “This is what the Lord, the God of Israel, says, ‘Every man fasten his sword to his side; go back and forth through the camp from entrance to entrance, and each of you kill his brother, his friend, and his neighbor.’”

28The Levites did as Moses commanded, and about three thousand men fell dead that day among the people.