Masechet Sanhedrin, Perek Yud Alef, Mishnah Hei: We will continue discussing the Aveirot (transgressions) that somebody would get Chenek (strangulation) for, namely a Navi Sheker (a false prophet).
The Mishnah says that a Navi Sheker, a false prophet, is somebody who says a prophecy in the name of Hashem but has never heard a prophecy; he’s making it all up. Or, a prophecy was said to somebody else, but he reports it in his own name. He’s put to death by the Bet Din (the human court); the human court puts him to death through Chenek, through strangulation.
But if somebody who’s actually a prophet holds back his prophecy—he was supposed to spread it to other people, but he never told anybody about it—or if somebody disregards the words of a Navi (a prophet), or if a Navi violates his own word—the prophecy that he received—and goes against it, he’s put to death by HaKadosh Baruch Hu, from the hands of heaven. He’s going to die an early death. As the Pasuk (verse) says, Hashem says, “I will demand from him.” Hashem is going to exact punishment on that person.