[133] And how, bhikkhus, does a bhikkhu dwell contemplating the body in the body?
Here, bhikkhus, a bhikkhu, gone to the forest, or gone to the root of a tree, or gone to an empty dwelling, sits down; having folded his legs crosswise, set his body erect, and established mindfulness before him, he breathes in just mindful, he breathes out mindful. Breathing in long, he knows clearly, 'I breathe in long'; breathing out long, he knows clearly, 'I breathe out long.' Breathing in short, he knows clearly, 'I breathe in short'; breathing out short, he knows clearly, 'I breathe out short.' He trains thus: 'Experiencing the whole body, I shall breathe in'; he trains thus: 'Experiencing the whole body, I shall breathe out.' He trains thus: 'Calming the bodily formation (kāyasaṅkhāra), I shall breathe in'; he trains thus: 'Calming the bodily formation, I shall breathe out.'
Just as, bhikkhus, a skilled turner or a turner's apprentice, when making a long pull, knows clearly, 'I make a long pull,' and when making a short pull, knows clearly, 'I make a short pull'—even so, bhikkhus, a bhikkhu, breathing in long, knows clearly, 'I breathe in long'; breathing out long, he knows clearly, 'I breathe out long.' Breathing in short, he knows clearly, 'I breathe in short'; breathing out short, he knows clearly, 'I breathe out short.' He trains thus: 'Experiencing the whole body, I shall breathe in'; he trains thus: 'Experiencing the whole body, I shall breathe out.' He trains thus: 'Calming the bodily formation, I shall breathe in'; he trains thus: 'Calming the bodily formation, I shall breathe out.'
Thus he dwells contemplating the body in the body internally, or he dwells contemplating the body in the body externally, or he dwells contemplating the body in the body both internally and externally. Or he dwells contemplating in the body the nature of origination (samudaya), or he dwells contemplating in the body the nature of vanishing, or he dwells contemplating in the body the nature of both origination and vanishing. Or else his mindfulness that 'there is a body' is established just to the extent necessary for knowledge (ñāṇa) and for continued mindfulness; and he dwells independent, and clings to nothing in the world. Thus too, bhikkhus, a bhikkhu dwells contemplating the body in the body.
The Section on Mindfulness of Breathing (ānāpānasati).
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.