Albert Barnes Commentary 1 Kings 22:30

"And the king of Israel said unto Jehoshaphat, I will disguise myself, and go into the battle; but put thou on thy robes. And the king of Israel disguised himself, and went into the battle." — 1 Kings 22:30 (ASV)

I will disguise myself - Ahab had probably heard of Ben-hadad’s order to his captains (1 Kings 22:31).