1 Kings 2:5-6

5Do not forget what Zeruiah's son Joab did to me. He killed the two leaders of Israel's armies, Ner's son Abner and Jether's son Amasa. Joab killed them as if they were his enemies in a war. But there was no war. So he is guilty of their deaths when they had done nothing wrong. Their blood is on his belt and on his shoes.

6So you should punish him in a way that you think is right. Do not let him die in peace as an old man.