Exodus 32:25-29

Moses saw that the people were acting wildly. Aaron had let them get out of control and become fools in front of their enemies. So Moses stood at the entrance to the camp and said, “Let anyone who wants to follow the LORD come to me.” And all the people from the family of Levi gathered around Moses. Then Moses said to them, “The LORD, the God of Israel, says this: ‘Every man must put on his sword and go through the camp from one end to the other. Each man must kill his brother, his friend, and his neighbor.’ ” The people from the family of Levi obeyed Moses, and that day about three thousand of the Israelites died. Then Moses said, “Today you have been given for service to the LORD. You were willing to kill your own sons and brothers, and God has blessed you for this.”