Numbers 25:18

For they antagonized you, etc., in the matter of Pe’or. Since they abandoned their daughters to promiscuity in order to cause you to stray after Pe’or. However, He did not order the destruction of Moav, Because of Rus [Ruth], who was destined to emanate from them, as we state in Bava Kama.

because they troubled you by their deceitful counsels when they beguiled you in the matter of Peor, and of Kosbi their sister, daughter of the prince of Midian, who was slain in the day of the plague for the matter of Peor.

FOR THEY [the Midianites] HARASS YOU BY THEIR WILES. The meaning [of the expression by their wiles] is, as I have explained, that this evil plan [to lead the Israelites astray through their seduction by the Moabite women] was contrived by the elders of Midian, as it is said, And Moab said unto the elders of Midian,, 22:4. [thus showing] that it was with them [the elders of Midian] that the Moabites originally took counsel. And they gave this advice [later on] to Moab, to encourage their daughters to prostitute themselves with them [the Israelites], and thereby cause them to join Baal-peor, and to draw them away from G-d, even though this advice is not [explicitly] mentioned there. Moreover, [a proof that the Midianites gave this idea to the Moabites is] that they even sent them their own king’s daughter to commit harlotry with them, this being the meaning of the expression, and in the matter of Cozbi, the daughter of the prince of Midian, their sister. For were this not done with the knowledge [and encouragement] of the counsellors of the [Midianite] kingdom, what was the distinguished Midianite princess seeking in Shittim, in the plains of Moab, that she should come to the camp of a foreign people, for Israel was in the plains of Moab, in Shittim, and how did this [important] Midianite woman come to be there? But [the only reasonable explanation of this is that] she was very beautiful, and therefore the elders of Midian sent her there, because they said: “Through the figure of a beautiful woman many people become corrupted.” It is probable that Balaam was also involved in [giving] this counsel, for on his return from the land of Moab [after he departed from Balak] he passed through Midian, from where he had come, and he deliberated with the counsellors of the kingdom. Perhaps Balaam stayed there a while in order to know what would [ultimately] happen to them [i.e., the Israelites], and that is why the Israelites found him in Midian and killed him. In that case the meaning [of the verse], And Balaam rose up, and went and returned to his place is that Balaam “went on his way [with the intention] of returning to his land” [but he did not actually get there, since he stayed on the way in Midian]. And it indeed appears so [that Balaam participated in giving this evil advice], for the Israelites would not have killed one who had prophesied except after [receiving a special] permission of the Torah [to do so, and we do not find …