Numbers 25:16-18 King James Version (KJV)
16 And the Lord spake unto Moses, saying,
17 Vex the Midianites, and smite them:
18 For they vex you with their wiles, wherewith they have beguiled you in the matter of Peor, and in the matter of Cozbi, the daughter of a prince of Midian, their sister, which was slain in the day of the plague for Peor's sake.
Numbers 25:16-18 New International Version (NIV)
16 The Lord said to Moses, 17 “Treat the Midianites as enemies and kill them. 18 They treated you as enemies when they deceived you in the Peor incident involving their sister Kozbi, the daughter of a Midianite leader, the woman who was killed when the plague came as a result of that incident.”