Retaliation: Joab on Abner
Source: Nav
2 Samuel 3:27, 30
When Abner returned to Hebron, Joab pulled him aside into the gateway, as if to speak to him privately, and there Joab stabbed him in the stomach. So Abner died on account of the blood of Joab’s brother Asahel. / (Joab and his brother Abishai murdered Abner because he had killed their brother Asahel in the battle at Gibeon.)