Deuteronomy 18:21-22

Revised Standard Version

²¹ And if you say in your heart, ‘How may we know the word which the Lord has not spoken?’— ²² when a prophet speaks in the name of the Lord, if the word does not come to pass or come true, that is a word which the Lord has not spoken; the prophet has spoken it presumptuously, you need not be afraid of him.