2 Samuel 3:24
Then Joab came to the king, and said, What hast thou done? behold, Abner came unto thee; why is it that thou hast sent him away, and he is quite gone? Then Joab came to the king, and said, What hast thou done? behold, Abner came unto thee; why is it that thou hast sent him away, and he is quite gone?
Abner had broken with the weak and incompetent Ishbosheth, been received by David, offered to bring all the tribes of Israel over to him, and been honorably dismissed to accomplish that transfer when the confrontation took place. The speaker who came to the king with the protest, asking what he had done and why he had sent Abner away so that he was quite gone, was Joab, commander-in-chief of David's army. His protest was motivated by jealousy at the favorable reception given to Abner as so valiant and famed a warrior.
It was also motivated by a blood feud because Abner had slain Joab's brother Asahel during the war between Israel and Judah, creating in Joab a desire to avenge his brother's death. It was further motivated by desire to get rid of Abner as a prospective rival. The confrontation led to Joab basely waylaying and murdering Abner. That treacherous murder overthrew the throne that malice and ambition had established.