Deuteronomy 18:20-22

Darby Translation

²⁰ But 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 gods, that prophet shall die.

²¹ And if thou say in thy heart, How shall we know the word that Jehovah hath not spoken?

²² When 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.