2 Samuel 3:26-27

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

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