C. F. Keil and Franz Delitzsch on 1 Kings 20:41-42

1Ki 20:41-42

Then the disciple of the prophets drew the bandage quickly from his eyes, so that the king recognised him as a prophet, and announced to him the word of the Lord: “Because thou hast let go out of thy hand the man of my ban (i.e., Benhadad, who has fallen under my ban), thy life shall stand for his life, and thy people for his people,” i.e., the destruction to which Benhadad was devoted will fall upon thee and thy people. The expression אישׁ־חרמי (man of my ban) showed Ahab clearly enough what ought to have been done with Benhadad. A person on whom the ban was pronounced was to be put to death (Lev 27:29).