2 Samuel 3:26-27

26Joab then left David and sent messengers after Abner, and they brought him back from the cistern at Sirah. But David did not know it.

27Now when Abner returned to Hebron, Joab took him aside into an inner chamber, as if to speak with him privately. And there, to avenge the blood of his brother Asahel, Joab stabbed him in the stomach, and he died.