2 Samuel 3:26-27

26Then Joab left David and sent messengers after Abner. They brought him back from the well of Sirah, but David was unaware of it.

27When Abner returned to Hebron, Joab pulled him aside to the middle of the city gate, as if to speak to him privately, and there Joab stabbed him in the stomach. So Abner died in revenge for the death of Asahel, Joab’s brother.