Deuteronomy 18:20-22

20But the prophet, which 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 say in thine heart, How shall we know the word which Yhwh hath not spoken?

22When a prophet speaketh in the name of Yhwh, if the thing follow not, nor come to pass, that is the thing which Yhwh hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him.