Deuteronomy 18:22 "You shall not fear him"

A person who announces that he is a prophet and then begins to declare his false prophecies can sometimes sound very convincing.

Just like others who lie, he is careful to say things that people want to hear, hoping they will believe that he is a true prophet and that what he says is true. Still there is no need to be afraid of his threats.

This Negative Mitzvah warns us not to fear the false prophet nor show any pity towards him.