Deuteronomy 18:20-22

20But the prophet who presumes to speak a word in My Name, which I have not commanded him to speak, or who speaks in the name of other gods—that prophet will die.’

21“Now should you say in your heart, ‘How would we recognize the word that Adonai has not spoken?’

22When a prophet speaks in Adonai’s Name and the word does not happen or come true, that is a word that Adonai has not spoken. The prophet has spoken it presumptuously—do not be afraid of him.