Deuteronomy 18:19-22

191And it shall come about that whoever does not listen to My words which he speaks in My name, I Myself will 2require it of him.

20But the prophet who speaks a word 3presumptuously in My name, a word which I have not commanded him to speak, or 4which he speaks in the name of other gods, 5that prophet shall die.’

21And if you say in your heart, ‘How will we recognize the word which the Lord has not spoken?’

226When the 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 7presumptuously; you are not to be afraid of him.