Deuteronomy 18:20-22

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.

21Now if you say to yourselves, ‘How can we tell that a message is not from the Lord?’ –

22whenever 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.”