Numbers 25:1, 6-8

While the people of Israel were still camped at Acacia, the men began sinning sexually with Moabite women.

Moses and the Israelites were gathered at the entrance to the Meeting Tent, crying there. Then an Israelite man brought a Midianite woman to his brothers in plain sight of Moses and all the people. Phinehas son of Eleazar, the son of Aaron, the priest, saw this, so he left the meeting and got his spear. He followed the Israelite into his tent and drove his spear through both the Israelite man and the Midianite woman. Then the terrible sickness among the Israelites stopped.