Albert Barnes Commentary 1 Kings 22:18

"And the king of Israel said to Jehoshaphat, Did I not tell thee that he would not prophesy good concerning me, but evil?" — 1 Kings 22:18 (ASV)

See 1 Kings 22:8. Ahab implies that he believes Micaiah spoke out of pure malevolence, without any authority from God for his prediction. By implication, he invites Jehoshaphat to disregard this pseudo-prophecy and to put his trust in the unanimous declaration of the 400. Micaiah, therefore, proceeds to explain the contradiction between himself and the 400 by recounting another vision.