Numbers 25:5 (KJV)

And Israel joined himself unto Baal–peor: and the anger of the Lord was kindled against Israel.

And the Lord said unto Moses, Take all the heads of the people, and hang them up before the Lord against the sun, that the fierce anger of the Lord may be turned away from Israel.

And Moses said unto the judges of Israel, Slay ye every one his men that were joined unto Baal–peor.

And, behold, one of the children of Israel came and brought unto his brethren a Midianitish woman in the sight of Moses, and in the sight of all the congregation of the children of Israel, who were weeping before the door of the tabernacle of the congregation.

And when Phinehas, the son of Eleazar, the son of Aaron the priest, saw it, he rose up from among the congregation, and took a javelin in his hand;