[26] Now at that time a certain bhikkhu, bitten by a snake, had died. They reported this matter to the Blessed One. …
"Surely, bhikkhus, that bhikkhu did not pervade the four royal families of snakes with a mind (citta) of loving-kindness (mettā). For if, bhikkhus, that bhikkhu had pervaded the four royal families of snakes with a mind of loving-kindness, then, bhikkhus, that bhikkhu, bitten by a snake, would not have died.
"Which are the four royal families of snakes? The Virūpakkha royal family of snakes, the Erāpatha royal family of snakes, the Chabyāputta royal family of snakes, and the Kaṇhāgotamaka royal family of snakes.
"Surely, bhikkhus, that bhikkhu did not pervade these four royal families of snakes with a mind of loving-kindness. For if, bhikkhus, that bhikkhu had pervaded these four royal families of snakes with a mind of loving-kindness, then, bhikkhus, that bhikkhu, bitten by a snake, would not have died.
"Bhikkhus, I allow you to pervade these four royal families of snakes with a mind of loving-kindness, for the guarding of oneself, for the protection of oneself, for making a safeguard (paritta) for oneself. And this, bhikkhus, is how it should be done:"
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.