2 Samuel 3:29-33

May it turn upon the head of Joab and on all his father’s house; and may there not be eliminated from the house of Joab someone who suffers a discharge, or has leprosy, or holds the spindle, or falls by the sword, or lacks bread.”

So Joab and his brother Abishai killed Abner because he had put their brother Asahel to death in the battle at Gibeon. David Mourns Abner

Then David said to Joab and to all the people who were with him, “Tear your clothes and put on sackcloth, and mourn before Abner.” And King David walked behind the bier.

And they buried Abner in Hebron; and the king raised his voice and wept at the grave of Abner, and all the people wept.

And the king sang a song of mourning for Abner and said, “Should Abner die as a fool dies?