Young's Literal Translation
19 and it hath been -- the man who doth not hearken unto My words which he doth speak in My name, I require [it] of him.
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? --Read full chapter