What did God give Phinehas for killing the inter-tribal couple in Numbers 25?

His covenant of peace

One of the children of Israel came and brought unto his brethren a Midianitish woman in the sight of Moses, and in the sight of all the congregation of the children of Israel ... And when Phinehas ... saw it, he ... took a javelin ... and thrust both of them through, the man of Israel, and the woman through her belly. So the plague was stayed from the children of Israel.

And the LORD spake unto Moses, saying, Phinehas ... hath turned my wrath away from the children of Israel, while he was zealous for my sake among them, that I consumed not the children of Israel in my jealousy. Wherefore say, Behold, I give unto him my covenant of peace. And he shall have it, and his seed after him, even the covenant of an everlasting priesthood; because he was zealous for his God, and made an atonement for the children of Israel. Numbers 25:6-13