2) Moreover, we do not believe in someone who claims that Elijah or the "grandfather of grandfathers" (a term referring to an ancient holy figure known as the "Supernal Crown") appeared to him. Such a person is undoubtedly a false prophet, and according to Jewish law, he would be sentenced to death by strangulation. This is explained in the introduction to the Mishneh Torah by Maimonides, specifically in his commentary on the section of Zera'im.
In the Gemara Pesachim 34a, there are different versions of a statement. The version of Rav Yochanan is: "She is rendered impure." Meaning, if Elijah were to come and declare her purity, stating that no impurity has come into contact with her, we would listen to him. However, according to Reish Lakish, he says: "She is rendered invalid."
If Elijah were to come and declare her purity, we would not listen to him. This is the explanation given by our Sages, namely, that "invalid" refers specifically to matters of sanctity, as they become disqualified through this. And the term "invalid" applies on its own. Even if Elijah were to come and say that all those who are ritually impure have become ritually pure, due to a distraction from their impurity, we would not listen to him.
This is the case unless a person has the authority to modify or permit a prohibition, even a rabbinical one, we do not listen to him.