Metamorphoses Book 3: Pentheus and Bacchus
Pentheus was a skeptical man who doubted Tiresias' prophecies, so when the blind man foretold that Pentheus would disrespect the power of Bacchus as a god and be ripped apart by the hands of his own mother and sisters for his faithlessness, Pentheus didn't believe him.
The skeptical man was angry at the way the citizens of Thebes rushed around in drunken frenzies in their worship of Bacchus. He set out to prove that Bacchus was not a real god, so he sent his men out to capture the imposter. When they returned, they had only a follower of the cult, and before Pentheus sentenced him to death, he asked him who he was and where he was from.
The man was Acoetes, a helmsman aboard the ship that tried to kidnap Bacchus. Acoetes was the only man among the crew who believed that Bacchus was a god and refused to take part in the kidnapping. When Bacchus turned the rest of the crew to dolphins, he spared Acoetes. The man then became Bacchus' follower.
Pentheus didn't believe the story, and so he sent the man to prison to be punished. While the instruments of torture were being prepared, Acoetes' cell was magically opened and his chains unlocked. Furious, Pentheus set out into the woods himself to find and capture the false god. When he stepped into a clearing, members of the Bacchus cult, including his own mother and sisters attacked him. Bacchus had infected them with madness that made Pentheus appear a boar to them, and though the man called out for help, he received no mercy at the hands of the worshippers.