Deuteronomy 18:18-22

I will raise up for them a prophet from among their countrymen like you, and I will put My words in his mouth, and he shall speak to them everything that I command him.

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

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

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

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