Numbers 25:1, 6-8

While Israel remained at Shittim, the people began to play the harlot with the daughters of Moab.

Then behold, one of the sons of Israel came and brought to his relatives a Midianite woman, in the sight of Moses and in the sight of all the congregation of the sons of Israel, while they were weeping at the doorway of the tent of meeting. When Phinehas the son of Eleazar, the son of Aaron the priest, saw it, he arose from the midst of the congregation and took a spear in his hand, and he went after the man of Israel into the tent and pierced both of them through, the man of Israel and the woman, through the body. So the plague on the sons of Israel was checked.