1 Kings 2:5-6

5“You know what Joab son of Zeruiah did to me – how he murdered two commanders of the Israelite armies, Abner son of Ner and Amasa son of Jether. During peacetime he struck them down like he would in battle; when he shed their blood as if in battle, he stained his own belt and the sandals on his feet.

6Do to him what you think is appropriate, but don’t let him live long and die a peaceful death.