Deuteronomy 18:20-22

20But if any prophet dares to speak a message in My name that I have not commanded him to speak, or to speak in the name of other gods, that prophet must be put to death.”

21You may ask in your heart, “How can we recognize a message that the LORD has not spoken?” 22When a prophet speaks in the name of the LORD and the message does not come to pass or come true, that is a message the LORD has not spoken. The prophet has spoken presumptuously. Do not be afraid of him.