Deuteronomy 18:20-22

Young's Literal Translation

²⁰ `Only, the prophet who presumeth to speak a word in My name -- that which I have not commanded him to speak -- and who speaketh in the name of other gods -- even that prophet hath died.

²¹ `And when thou sayest in thy heart, How do we know the word which Jehovah hath not spoken? --

²² that which the prophet speaketh in the name of Jehovah, and the thing is not, and cometh not -- it [is] the word which Jehovah hath not spoken; in presumption hath the prophet spoken it; -- thou art not afraid of him.