Exodus 32:28 KJV

26Then Moses stood in the gate of the camp, and said, Who is on the LORD’s side? let him come unto me. And all the sons of Levi gathered themselves together unto him.

27And he said unto them, Thus saith the LORD God of Israel, Put every man his sword by his side, and go in and out from gate to gate throughout the camp, and slay every man his brother, and every man his companion, and every man his neighbour.

28And the children of Levi did according to the word of Moses: and there fell of the people that day about three thousand men.

29For Moses had said, Consecrate yourselves today to the LORD, even every man upon his son, and upon his brother; that he may bestow upon you a blessing this day.

30And it came to pass on the morrow, that Moses said unto the people, Ye have sinned a great sin: and now I will go up unto the LORD; peradventure I shall make an atonement for your sin.