2 Samuel 20:10-13

He smote him— This action was attended with the highest perfidy and insolence. Many reasons concurred to prevent David's calling him to an account now; particularly his power, authority, and interest with the army: but it is plain that he never forgot this outrage of Joab's. 'That he highly resented it, we find in his last charge to Solomon, where he recommends and gives it in charge to his son to do justice on that bloody assassin. He was not now in a capacity to do it. Joab was too powerful a subject to be brought to account. After Absalom's death, he had the insolence to tell the king with an oath, that he would make every one of his subjects desert him; and after this assassination of Amasa, he resumed, contrary to his master's will, the command of all the forces, who had an affection for him as their own general, because he had restored the quiet of the land by quelling the insurrection of Sheba. Joab's being continued captain-general of all the forces, was not from David's inclination, but contrary to it, and by force.