Deuteronomy 18:20-22

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