Deuteronomy 18:20-22

18:20 “But if any prophet presumes to speak anything in my name that I have not authorized him to speak, or speaks in the name of other gods, that prophet must die. 18:21 Now if you say to yourselves, ‘How can we tell that a message is not from the Lord?’ – 18:22 whenever a prophet speaks in my name and the prediction is not fulfilled, then I have not spoken it; the prophet has presumed to speak it, so you need not fear him.”