2 Samuel 3:27-30

27So when Abner returned to Hebron, Joab took him aside to the middle of the gate to speak to him privately, and there he struck Abner in the abdomen so that he died, to avenge the blood of Asahel, Joab’s brother.

28Afterward, when David heard of it, he said, “I and my kingdom are forever innocent before the Lord of the blood of Abner the son of Ner.

29Let the guilt fall on the head of Joab and on all his father’s house (family); and may there never disappear from the house of Joab one who suffers with a discharge or one who is a leper or one who walks with a crutch [being unfit for war], or one who falls by the sword, or one who lacks food.”

30So Joab and Abishai his brother murdered Abner because he had killed their brother Asahel in the battle at Gibeon.