Exodus 32:26-30

Moses then stood at the gate of the camp, and said, “Whoever is for the Lord, come to me!” And all the sons of Levi gathered together to him.

And he said to them, “This is what the Lord, the God of Israel says: ‘Every man of you put his sword on his thigh, and go back and forth from gate to gate in the camp, and kill every man his brother, and every man his friend, and every man his neighbor.’ ”

So the sons of Levi did as Moses instructed, and about three thousand men of the people fell that day.

Then Moses said, “Dedicate yourselves today to the Lord—for every man has been against his son and against his brother—in order that He may bestow a blessing upon you today.”

And on the next day Moses said to the people, “You yourselves have committed a great sin; and now I am going up to the Lord; perhaps I can make atonement for your sin.”