Āsīvisopamasutta
“Seyyathāpi, bhikkhave, cattāro āsīvisā uggatejā ghoravisā. Atha puriso āgaccheyya jīvitukāmo amaritukāmo sukhakāmo dukkhappaṭikūlo. Tamenaṁ evaṁ vadeyyuṁ: ‘ime te, ambho purisa, cattāro āsīvisā uggatejā ghoravisā kālena kālaṁ vuṭṭhāpetabbā, kālena kālaṁ nhāpetabbā, kālena kālaṁ bhojetabbā, kālena kālaṁ saṁvesetabbā. Yadā ca kho te, ambho purisa, imesaṁ catunnaṁ āsīvisānaṁ uggatejānaṁ ghoravisānaṁ aññataro vā aññataro vā kuppissati, tato tvaṁ, ambho purisa, maraṇaṁ vā nigacchasi, maraṇamattaṁ vā dukkhaṁ. Yaṁ te, ambho purisa, karaṇīyaṁ taṁ karohī’ti.
The Simile of the Vipers
“Mendicants, suppose there were four venomous vipers of awesome might. Then a person would come along who wants to live and doesn’t want to die, who wants to be happy and recoils from pain. They’d say to him, ‘My man, here are four venomous vipers of awesome might. They must be periodically picked up, washed, fed, and put to sleep. But when one or other of these four venomous vipers gets angry with you, you’ll meet with death or deadly pain. So then, my man, do what has to be done.’