Exodus 32:31 (KJV)

Then 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.

And 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.

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

For 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.

And 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.

Yet now, if thou wilt forgive their sin--; and if not, blot me, I pray thee, out of thy book which thou hast written.

And the LORD said unto Moses, Whosoever hath sinned against me, him will I blot out of my book.

Therefore now go, lead the people unto the place of which I have spoken unto thee: behold, mine Angel shall go before thee: nevertheless in the day when I visit I will visit their sin upon them.

And the LORD plagued the people, because they made the calf, which Aaron made.