By some prophet; that we may know the mind of God in it, and what success we may expect. This was the practice of the godly. See Judges 1:1, Judges 20:28 1 Samuel 23:2.
Related Commentaries of 1 Kings 22:5
1 Kings 22:5
5 And Jehoshaphat said unto the king of Israel, Enquire, I pray thee, at the word of the LORD to day.