[309] Thus have I heard. On one occasion the Blessed One was dwelling at Sāvatthī, in Jeta's Grove. Then the Blessed One addressed the bhikkhus: "Bhikkhus, suppose there were four vipers (āsīvisa) of fierce heat and horrible venom. Then a man would come along, wishing to live, not wishing to die, desiring happiness, averse to suffering (dukkha). They would say to him: 'Good man, these four vipers of fierce heat and horrible venom must from time to time be roused, from time to time bathed, from time to time fed, from time to time put back into their den. And when, good man, one or another of these four vipers of fierce heat and horrible venom becomes provoked, then, good man, you will meet with death or with deadly suffering. Whatever, good man, is to be done by you — do that.'"
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.