Midrasz do Diwrej ha-jamim II 18:10

Our Rabbis were taught: There are three [in connection with prophecy] who are to be sentenced by court; viz., he who prophesies what he has not heard — e.g., Zedekiah ben Kenaanah, of whom it is written (II Chron. 18, 10) Made himself horns of iron, etc. But why was he guilty? Did not the spirit of Nabeth make him err, as it is written (Ib., ib. 19-21) And the Lord said, Who will persuade Achab, the king of Israel, that he may go up and fall at Ramoth-gilead? And one spake saying after this manner, and another saying after that manner. Then came forth, a spirit, and placed himself before the Lord, and said, I will persuade him. And the Lord said unto him. Wherewith? And he said, I will go forth and I will become a lying spirit in the mouth of all his prophets. And he said. Thou shalt persuade him, and also prevail; go forth and do so. What is meant by go forth? R. Juda said: "Go outside of My compartment as a liar cannot remain in it." And to the question: What spirit? R. Jochanan said: "The spirit of Naboth Ha-Israeli." [Hence it was not Zedekiah's fault, as he was deceived by the spirit] He ought to have given his attention to what was said by R. Isaac: "The same watchword [divine oracle] is passed to many prophets, but no two prophets prophecy under the same watchwords (use the very same expressions); e.g., (Ob. 1, 3) The presumption of thy heart hath beguiled thee. (Jer. 49, 16) Thy haste hath deceived thee — the presumption of thy heart. Here, however, it reads (II. Chron. 18, 11) And all the' prophets so prophesied, saying. Go up against Ramoth-gilead. etc." Hence, as all prophesied in identical language, he ought to have known that it was not a true prophecy. But perhaps Zedekiah did not know what was said by R. Isaac. There was Jehoshaphat, who told him that, as it is written (Ib., ib. 6) Is there not a prophet of the Eternal besides? And to the question of Achab: Are not all these who prophesy in the name of the Lord sufficient? Jehoshaphat answered: "I have a tradition from my grandfather's house that the same watch-word [divine oracle] is passed to many prophets, but two prophets cannot prophesy under the same watchword using the very same expression."