Exodus 32:27-29

27And 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.’ ”

28So the sons of Levi did according to the word of Moses. And about three thousand men of the people fell that day.

29Then 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.”