Deuteronomy 18:20-22

But if a prophet says something I did not tell him to say as though he were speaking for me, or if a prophet speaks in the name of other gods, that prophet must be killed.” You might be thinking, “How can we know if a message is not from the LORD?” If what a prophet says in the name of the LORD does not happen, it is not the LORD’s message. That prophet was speaking his own ideas. Don’t be afraid of him.