2 Samuel 3:37

For all the people and all Israel understood that day that it was not of the king to slay Abner the son of Ner.

On that day all the people and all Israel became convinced that the slaying of Abner son of Ner was not from the king and that David had no part in it. That conviction came because David magnanimously honored one who had been his bitter enemy, and all that he did in mourning Abner pleased the nation. By that honoring of Abner he won the confidence and admiration of all the people. In his mourning he called Abner a prince and a great man fallen in Israel. Though anointed king he acknowledged that he was weak and that the sons of Zeruiah were too hard for him to punish as he desired, so he left the murderers to the justice of God for the Lord to reward the doer of evil according to his wickedness.