Deuteronomy 18:20-22

But the prophet who presumes to speak a word in My name which I have not commanded him to speak, or which he speaks in the name of other gods—that prophet shall die.’ If you say in your heart, ‘How will we know and recognize the word which the LORD has not spoken?’ When a prophet speaks in the name of the LORD and the thing does not happen or come true, that is the thing which the LORD has not spoken. The prophet has spoken it presumptuously; you shall not be afraid of him.