2Sam 3:26-30

26When Joab came out from David's presence, he sent messengers after Abner, and they brought him back from the cistern of Sirah; but David did not know about it.27When Abner returned to Hebron, Joab took him aside in the gateway to speak with him privately, and there he stabbed him in the stomach. So he died for shedding the blood of Asahel, Joab's brother.28Afterward, when David heard of it, he said, “I and my kingdom are forever guiltless before the Lord for the blood of Abner son of Ner.29May the guilt fall on the head of Joab, and on all his father's house; and may the house of Joab never be without one who has a discharge, or who is leprous, or who holds a spindle, or who falls by the sword, or who lacks food!”30So Joab and his brother Abishai murdered Abner because he had killed their brother Asahel in the battle at Gibeon.