2 Samuel 3:30-31

30That is how Joab and his brother Abishai killed Abner. They killed him because he had killed their brother Asahel in the battle at Gibeon.

31David said to Joab and to all the people who were with him, ‘Tear your clothes! Wear sackcloth to show that you are sad! Weep because of Abner's death.’ King David himself walked behind the men who carried Abner's dead body.