1 Kings 2:5

Also, you know what Joab, the son of Zeruiah, has done to me, what he did to the two leaders of the army of Israel, to Abner, the son of Ner, and to Amasa, the son of Jether. He killed them, and so he shed the blood of war in peace time, and he set the bloodshed of battle on his belt, which was around his waist, and in his shoes, which were on his feet.