Exodus 32:25-29

25Moses saw that the people were running wild, for Aaron had let them get completely out of control, causing derision from their enemies.

26So Moses stood at the entrance of the camp and said, “Whoever is for the Lord, come to me.” All the Levites gathered around him,

27and he said to them, “Thus says the Lord, the God of Israel, ‘Each man fasten his sword on his side, and go back and forth from entrance to entrance throughout the camp, and each one kill his brother, his friend, and his neighbor.’”

28The Levites did what Moses ordered, and that day about three thousand men of the people died.

29Moses said, “You have been consecrated today for the Lord, for each of you was against his son or against his brother, so he has given a blessing to you today.”