Deuteronomy 18:22
When a prophet speaketh in the name of the LORD, if the thing follow not, nor come to pass, that is the thing which the LORD hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him. When a prophet speaketh in the name of the LORD, if the thing follow not, nor come to pass, that is the thing which the LORD hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him.
This standard was given to ancient Israel through Moses. The power to make known the past and the future sets the true God apart from every false god. It provides one of the divinely appointed tests of a true prophet of God, namely the accurate fulfillment of what is spoken in the name of the Lord.
When a man speaks in the name of the Lord, what he predicts must happen. If the thing does not follow nor come to pass, that proves the Lord did not speak it but the prophet spoke it presumptuously. Such a prophet is not to be feared, and the failure marks him as false. When an announced time passes without the predicted events, the claimant is proved a false prophet and the visions false.