John Wesley on 2 Samuel 21:6

I will - Having doubtless consulted God in the matter; who as he had before declared Saul's bloody house to be the causes of this judgment, so now commanded that justice should be done upon it, and that the remaining branches of it should be cut off; as sufficiently appears from hence, that God was well pleased with the action; which he would not have been, if David had done it without his command; for then it had been a sinful action of David's, and contrary to a double law of God, Deut 21:23 24:16.