Exodus 32:25-29

25Moses saw that Aaron had let the people get completely out of control, much to the amusement of their enemies.

26So he stood at the entrance to the camp and shouted, “All of you who are on the Lord’s side, come here and join me.” And all the Levites gathered around him.

27Moses told them, “This is what the Lord, the God of Israel, says: Each of you, take your swords and go back and forth from one end of the camp to the other. Kill everyone—even your brothers, friends, and neighbors.”

28The Levites obeyed Moses’ command, and about 3,000 people died that day.

29Then Moses told the Levites, “Today you have ordained yourselves for the service of the Lord, for you obeyed him even though it meant killing your own sons and brothers. Today you have earned a blessing.”