Deuteronomy 18:20-22

20But the prophet, who shall presume to speak a word in my name, which I have not commanded him to speak, or that shall speak in the name of other gods, even that prophet shall die. 21And if thou shalt say in thy heart, How shall we know the word which the LORD hath not spoken? 22When a prophet speaketh in the name of the LORD, if the thing doth not follow, nor come to pass, that is the thing which the LORD hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him.