[320] "Bhikkhus, once in the past a tortoise (kumma kacchapa) was intent on searching for food along the riverbank in the evening. And a jackal (sigāla), too, bhikkhus, was intent on searching for food along the riverbank in the evening. The tortoise, bhikkhus, saw the jackal from afar, intent on its search for food; having seen it, it drew its limbs — the neck being the fifth — into its own shell, and remained passive and silent, keeping still. The jackal, too, bhikkhus, saw the tortoise from afar, intent on its search for food; having seen it, it approached the tortoise, and having approached, it stood waiting near the tortoise, [thinking]: 'When this tortoise extends one or another of its limbs, the neck being the fifth, right there I will seize it, tear it out, and devour it.' But when, bhikkhus, the tortoise did not extend any one of its limbs with the neck as fifth, then the jackal, not gaining an opening (otāra), lost interest in the tortoise and departed.
"Even so, bhikkhus, Māra the Evil One is constantly and continually waiting near you too, [thinking]: 'Perhaps I may gain an opening through the eye of these [bhikkhus] … or perhaps I may gain an opening through the tongue … or perhaps I may gain an opening through the mind.' Therefore, bhikkhus, dwell with the doors guarded in the sense faculties (indriya). Having seen a form with the eye, do not grasp at its sign (nimitta), do not grasp at its features (anubyañjana). Since, if one dwells with the eye faculty unrestrained, evil unwholesome states of covetousness and grief regarding the world (abhijjhā-domanassa) might flow in upon one, practise for its restraint; guard the eye faculty; undertake restraint of the eye faculty. Having heard a sound with the ear … Having smelled an odour with the nose … Having tasted a flavour with the tongue … Having touched a tangible with the body … Having cognized a dhamma with the mind, do not grasp at its sign, do not grasp at its features. Since, if one dwells with the mind faculty unrestrained, evil unwholesome states of covetousness and grief might flow in upon one, practise for its restraint; guard the mind faculty; undertake restraint of the mind faculty. When, bhikkhus, you dwell with the doors guarded in the sense faculties, then Māra the Evil One, not gaining an opening, will lose interest in you and depart, just as the jackal did from the tortoise."
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.