Halakhah zu Dewarim 13:4

To not listen to one who prophecies in the name of idolatry: That we not listen [to] the prophecy of one who prophecies in the name of idolatry - meaning to say that we not ask him for, and investigate him with, a sign or wonder about his prophecy, as we do with one who prophecies in the name of God. Rather we prevent him from the thing, as is fitting with any criminal or guilty one. And if he persists in his evil, we apply the well-known punishment for which the Torah makes him liable, and that is to kill him with strangulation. And about this is it stated (Deuteronomy 13:4), "You shall not listen to the words of that prophet."