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Deu 18:21 And if thou say in thine heart, How shall we know the word which the LORD hath not spoken?
Deu 18:22 When a prophet speaketh in the name of the LORD, if the thing follow not, nor come to pass, that is the thing which the LORD hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him.
Here's the New World Translation, straight off the Watchtower website:
20 “‘However, the prophet who presumes to speak in my name a word that I have not commanded him to speak or who speaks in the name of other gods, that prophet must die. 21 And in case you should say in your heart: “How shall we know the word that Jehovah has not spoken?” 22 when the prophet speaks in the name of Jehovah and the word does not occur or come true, that is the word that Jehovah did not speak. With presumptuousness the prophet spoke it. You must not get frightened at him.’
As you can plainly see in Deu 18:20, the Watchtower Bible and Tract Society is totally F-d'.