Albert Barnes Commentary Psalms 7:4

"If I have rewarded evil unto him that was at peace with me; (Yea, I have delivered him that without cause was mine adversary;)" — Psalms 7:4 (ASV)

If I have rewarded evil unto him that was at peace with me - If I have done evil, or if I have repaid him who was friendly with some unjust and evil conduct. If I have come upon him maliciously and unprovoked, and have done him wrong. This seems to have been the substance of the accusation; and, as remarked above, it is most probable that the accuser (Cush) referred to himself.

Yea, I have delivered him that without cause is mine enemy - So far is this from being true, that the very reverse is true. So far from taking advantage of another who was at peace with me, and depriving him of his just rights by fraud or force, it is a fact that I have rescued from impending danger the man who was at war with me, and who was an avowed enemy.

It would seem probable that in this he refers to this very Cush, and means to say that there was some occasion when Cush, who had long been hostile to David, was entirely in David's power, and when David not only declined to take advantage of Cush but actually intervened to rescue him from danger.

An instance of this kind actually occurred in the life of David, in his treatment of Saul (1 Samuel 24:10–11); and it is possible that David referred to that case, and meant to say that that was an indication of his character, and of his manner of treating others.

Those who suppose that the whole psalm refers to Saul (see the introduction, Section 2), of course regard this as the specific case referred to. There may have been other instances of the same kind in the life of David, and there is no improbability in supposing that on some occasion he had treated this very man, “Cush,” in this way, and that he refers here to that fact.