Deuteronomy 18:19-22

19And it shall come to pass that the man who hearkeneth not unto my words which he shall speak in my name, I will require it of him. 20But the prophet who shall presume to speak a word in my name that I have not commanded him to speak, or that shall speak in the name of other 1gods, that prophet shall die. 21And if thou say in thy heart, How shall we know the word that Jehovah hath not spoken? 22When a prophet speaketh in the name of Jehovah, and the thing followeth not, nor cometh to pass, that is the word which Jehovah hath not spoken; the prophet hath spoken it presumptuously: be not afraid of him.