Deuteronomy 13:5, 9

The prophets or dreamers must be killed, because they said you should turn against the LORD your God, who brought you out of Egypt and saved you from the land where you were slaves. They tried to turn you from doing what the LORD your God commanded you to do. You must get rid of the evil among you.

You must put them to death. You must be the first one to start to kill them, and then everyone else must join in.