NET Bible
"When Abner returned to Hebron, Joab took him aside at the gate as if to speak privately with him. Joab then stabbed him in the abdomen and killed him, avenging the shed blood of his brother Asahel."
— 2 Samuel 3:27, NET Bible
“And when Abner was returned to Hebron, Joab took him aside in the gate to speak with him quietly, and smote him there under the fifth rib, that he died, for the blood of Asahel his brother.”
“And when Abner was returned to Hebron, Joab took him aside into the midst of the gate to speak with him quietly, and smote him there in the body, so that he died, for the blood of Asahel his brother. ”
“When Abner was returned to Hebron, Joab took him aside into the midst of the gate to speak with him quietly, and struck him there in the body, so that he died, for the blood of Asahel his brother.”
“And when Abner was returned to Hebron, Joab took him aside to the middle of the gate, to speak to him treacherously: and he stabbed him there in the groin, and he died, in revenge of the blood of Asael his brother.”
“And when Abner was back in Hebron, Joab took him on one side by the doorway of the town to have a word with him quietly, and there he gave him a wound in the stomach, causing his death in payment for the death of his brother Asahel.”
“And when Abner was returned to Hebron, Joab took him aside in the gate to speak with him quietly, and smote him there under the fifth rib, that he died, for the blood of Asahel his brother.”
So Joab went to the king and said,“What have you done? Abner has come to you! Why would you send him away? Now he’s gone on his way!
You know Abner the son of Ner! Surely he came here to spy on you and to determine when you leave and when you return and to discover everything that you are doing!”
Then Joab left David and sent messengers after Abner. They brought him back from the well of Sirah.(But David was not aware of it.)
When Abner returned to Hebron, Joab took him aside at the gate as if to speak privately with him. Joab then stabbed him in the abdomen and killed him, avenging the shed blood of his brother Asahel.
When David later heard about this, he said,“I and my kingdom are forever innocent before the LORD of the shed blood of Abner son of Ner!
May his blood whirl over the head of Joab and the entire house of his father! May the males of Joab’s house never cease to have someone with a running sore or a skin disease or one who works at the spindle or one who falls by the sword or one who lacks food!”
So Joab and his brother Abishai killed Abner, because he had killed their brother Asahel in Gibeon during the battle.