So Joab and Abishai his brother killed Abner, because he had put their brother Asahel to death in the battle at Gibeon.
We have here an account of the murder of Abner by Joab, and David's deep resentment of it. I. Joab very insolently fell foul upon David for treating with Abner. He happened to be abroad upon service when Abner was with David, pursuing a troop, either of Philistines or of Saul's party; but, upon his return, he was informed that Abner was just gone (Sa2...
Commenting on 2 Samuel 3:22-39
So Joab and Abishai his brother slew Abner,.... For though it was only Joab that gave him the thrust of which he died, Abishai was in the secret, and was consenting and advising to his death, and so an accessory to it; and might be present, ready to assist in it, if occasion required; and so Josephus (k) expressly says, that Abishai his brother was...
So Joab and Abishai his brother slew Abner, because he had slain their brother Asahel at Gibeon in the battle. (l) Abishai is said to slay him with Joab, because he consented to the murder.