[197] "Sir Bhāradvāja, for those bhikkhus who are developed in body, developed in virtue, developed in mind, and developed in wisdom, that is not difficult; but, sir Bhāradvāja, for those bhikkhus who are undeveloped in body, undeveloped in virtue, undeveloped in mind, and undeveloped in wisdom, that is difficult. Sometimes, sir Bhāradvāja, though one thinks, 'We shall attend to it as unattractive (asubha),' it comes to one only as attractive (subha). Is there, sir Bhāradvāja, any other cause, any other condition, whereby these young bhikkhus, youthful, with jet-black hair … and maintain it for the full course?"
"This has been said, great king, by the Blessed One who knows and sees, the Arahant, the Perfectly Awakened One: 'Come, bhikkhus, dwell with the doors guarded in regard to the sense faculties (indriya). Having seen a form with the eye, do not be graspers of the sign (nimitta), do not be graspers of the features (anubyañjana). Since, if one dwells with the eye faculty unrestrained, evil, unwholesome states of covetousness and grief (abhijjhā-domanassa) might flow in upon one, practise for its restraint (saṃvara); guard the eye faculty; undertake restraint over the eye faculty. Having heard a sound with the ear … Having smelt an odour with the nose … Having savoured a taste with the tongue … Having touched a tangible with the body … Having cognized a mental phenomenon (dhamma) with the mind, do not be graspers of the sign, do not be graspers of the 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 over the mind faculty.' This too, great king, is a cause, this a condition, whereby these young bhikkhus, youthful, with jet-black hair, endowed with the blessing of youth, in the first stage of life, who have not dallied with sensual pleasures, lead the holy life (brahmacariya) complete and pure for as long as they live, and maintain it for the full course."
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.