On one occasion the Venerable Sāriputta was dwelling at Savatthī in Jeta’s Grove, Anathapiṇḍika’s Park. Then a certain bhikkhu approached the Venerable Sāriputta and exchanged greetings with him. When they had concluded their greetings and cordial talk, he sat down to one side and said to the Venerable Sāriputta:
“Friend Sāriputta, a bhikkhu who was my co-resident has given up the training and returned to the lower life.”
“So it is, friend, when one does not guard the doors of the sense faculties, is immoderate in eating, and is not devoted to wakefulness. That a bhikkhu who does not guard the doors of the sense faculties, who is immoderate in eating, sn.iv.104 and who is not devoted to wakefulness will maintain all his life the complete and pure holy life—this is impossible. But, friend, that a bhikkhu who guards the doors of the sense faculties, who is moderate in eating, and who is devoted to wakefulness will maintain all his life the complete and pure holy life—this is possible.
“And how, friend, does one guard the doors of the sense faculties? Here, having seen a form with the eye, a bhikkhu does not grasp its signs and features. Since, if he left the eye faculty unrestrained, evil unwholesome states of covetousness and displeasure might invade him, he practises the way of its restraint, he guards the eye faculty, he undertakes the restraint of 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 felt a tactile object with the body … Having cognized a mental phenomenon with the mind, a bhikkhu does not grasp its signs and features. Since, if he left the mind faculty unrestrained, evil unwholesome states of covetousness and displeasure might invade him, he practises the way of its restraint, he guards the mind faculty, he undertakes the restraint of the mind faculty. It is in this way, friend, that one guards the doors of the sense faculties.
“And how, friend, is one moderate in eating? Here, reflecting carefully, a bhikkhu takes food neither for amusement nor for intoxication nor for the sake of physical beauty and attractiveness, but only for the support and maintenance of this body, for ending discomfort, and for assisting the holy life, considering: ‘Thus I shall terminate the old feeling and not arouse a new feeling, and I shall be healthy and blameless and live in comfort.’ It is in this way, friend, that one is moderate in eating.
“And how, friend, is one devoted to wakefulness? Here, during the day, while walking back and forth and sitting, a bhikkhu purifies his mind of obstructive states. In the first watch of the night, while walking back and forth and sitting, he purifies his mind of obstructive states. sn.iv.105 In the middle watch of the night he lies down on his right side in the lion’s posture with one foot overlapping the other, mindful and clearly comprehending, after noting in his mind the idea of rising. After rising, in the last watch of the night, while walking back and forth and sitting, he purifies his mind of obstructive states. It is in this way, friend, that one is devoted to wakefulness.
“Therefore, friend, you should train yourself thus: ‘We will guard the doors of the sense faculties; we will be moderate in eating; we will be devoted to wakefulness.’ Thus, friend, should you train yourself.”