And it shall be for him and for his seed after him a covenant of eternal priesthood, because he was jealous for his God and made atonement for the children of Yisrael.
Torah Temimah: Yerushalmi Sanhedrin 9:7
Sefaria — Yerushalmi Sanhedrin 9:7
English: One who cohabits with an Aramis — zealots may strike him. It was taught: not by the will of the Sages; and Pinchas [acted] not by the will of the Sages. R. Yudah ben Pazi said: they sought to place him in nidui, had not the Divine Spirit leapt forth and said “and it shall be for him and for his seed after him a covenant of eternal priesthood.”
Limits of kanaus and divine ratification.
The law of kana’im is not a beis-din initiative; Pinchas was nearly banned until Heaven confirmed him.