Deuteronomy 18:20-22

20But a prophet who presumes to speak in my name anything I have not commanded, or a prophet who speaks in the name of other gods, is to be put to death.”

21You may say to yourselves, “How can we know when a message has not been spoken by the Lord?”

22If what a prophet proclaims in the name of the Lord does not take place or come true, that is a message the Lord has not spoken. That prophet has spoken presumptuously, so do not be alarmed.