Halakhah su Numeri 31:16

From the laws of the commandment is that which they, may their memory be blessed, said (Sanhedrin 81a) that zealots would attack one who has sexual intercourse with an Aramean (gentile) publicly in the eyes of ten or more Israelites. And the proof of the thing is the story of Pinchas and Zimri. But the zealot is nonetheless only permitted to attack him at the time of the promiscuous act, and like in the story that happened; as it is stated (Numbers 25:8), "and the woman through her belly." But if he separated [from her], we do not kill him, but [rather] bring him to the court and they administer lashes [upon] him, since he did the act publicly. [If] the zealots did not attack him and the court did not administer lashes [upon] him, we know from the words of tradition that he is [punished] by excision, as it is written (Malachi 2:11-12), "and he who husbands (read here as, who has sexual intercourse with) the daughter of a foreign god. The Lord will excise the man that does it." And a gentile who has sexual relations with an Israelite - if she is a married woman, he is killed over her; but, if not, he is not killed. But a Jew who wantonly has sexual relations with a gentile woman - even [if it is] by way of harlotry - she is nonetheless killed, since a mishap happened to an Israelite through her, like the law of an animal. And this thing is explicit in the Torah, as it is stated (Numbers 31:16-17), "They were the ones that were with the word of Bilaam against the Children of Israel, etc. and any woman that could know a man sexually they killed." [This] and the rest of its details are elucidated in Avodah Zarah and Yevamot and Kiddushin (see Mishneh Torah, Laws of Forbidden Intercourse 2).