2 Samuel 3:30

Overview - 2 Samuel 3
1	During the war David still waxes stronger.
2	Six sons are born to him in Hebron.
6	Abner, displeased with Ish-bosheth,
7	revolts to David.
13	David requires as a condition to bring him his wife Michal.
17	Abner, having communed with the Israelites, is feasted by David, and dismissed.
22	Joab returning from battle, is displeased with the king, and kills Abner.
28	David curses Joab;
31	and mourns for Abner.

2 Samuel 3:30  (King James Version)
So Joab and Abishai his brother slew Abner, because he had slain their brother Asahel at Gibeon in the battle.