“Fiendfyre — cursed fire — it’s one of the substances that destroy Horcruxes, but I would never, ever have dared use it, it’s so dangerous — how did Crabbe know how to — ?”
“Must’ve learned it from the Carrows,” said Harry grimly.
“Shame he wasn’t concentrating when they mentioned how to stop it, really,” said Ron, whose hair, like Hermione’s, was singed, and whose face was blackened. “If he hadn’t tried to kill us all, I’d be quite sorry he was dead.”
Harry Potter and the Deathly Hallows – J.K. Rowling