2 Samuel 3:24-27

24Then Joab came to the king and said, “What have you done? Behold, Abner came to you; why did you send him away, so that he is already gone?

25You know Abner the son of Ner, that he [only] came to deceive you [with flattering words] and to learn of your going out and coming in, and to find out what you are doing.”

26When Joab left David, he sent messengers after Abner, and they brought him back from the well of Sirah; but David knew nothing [about Joab’s action].

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.