[38] Then that nāga saw that the Blessed One had entered; and having seen him, pained and dejected, it sent forth smoke. Then it occurred to the Blessed One: "What if I, without harming this nāga's outer skin, hide, flesh, sinews, bones, or bone-marrow, were to master its fire with fire?" Then the Blessed One, having performed a feat of psychic power (iddhābhisaṅkhāra) of such a kind, sent forth smoke. Then that nāga, unable to bear the affront, blazed forth. The Blessed One too, having attained the fire element (tejodhātu), blazed forth. As both were in flames, the fire chamber appeared as though burning, blazing, all aflame. Then those matted-hair ascetics (jaṭila), surrounding the fire chamber, said this: "The great ascetic is truly handsome, sirs — yet he is being harmed by the nāga!" Then, at the end of that night, the Blessed One, having mastered that nāga's fire with fire without harming its outer skin, hide, flesh, sinews, bones, or bone-marrow, placed it in his bowl and showed it to Uruvelakassapa the matted-hair ascetic, saying: "Here, Kassapa, is your nāga; its fire has been mastered by fire." Then it occurred to Uruvelakassapa the matted-hair ascetic: "The great ascetic is truly of great psychic power, of great might, in that he could master with fire the fire of that fierce nāga king, possessed of psychic power, a venomous serpent of terrible venom. But he is certainly not an arahant, as I am."
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.