[417] How does one train thus: 'Contemplating fading away (virāgānupassī), I shall breathe out'; how does one train thus: 'Contemplating fading away, I shall breathe in'?
Having seen the danger (ādīnava) in form (rūpa), one becomes one in whom desire (chanda) has arisen for the fading away of form; one is resolved through faith (saddhādhimutta), and one's mind (citta) is well steadied; one trains thus: 'Contemplating fading away in form, I shall breathe out'; one trains thus: 'Contemplating fading away in form, I shall breathe in.' Having seen the danger in feeling (vedanā), in perception, in volitional formations, in consciousness, in the eye … in aging and death, one becomes one in whom desire has arisen for the fading away of aging and death; one is resolved through faith, and one's mind is well steadied; one trains thus: 'Contemplating fading away in aging and death, I shall breathe out'; one trains thus: 'Contemplating fading away in aging and death, I shall breathe in.' Through contemplating fading away, by way of the out-breaths and in-breaths, dhammas are the establishment (upaṭṭhāna); mindfulness (sati) is the knowledge (ñāṇa) of contemplation. The dhammas are the establishment, they are not the mindfulness; mindfulness is both the establishment and mindfulness itself. With that mindfulness and that knowledge one contemplates those dhammas. Therefore it is said: 'the development of the establishment of mindfulness (satipaṭṭhāna) as contemplation of dhammas in dhammas.'
'One contemplates': how does one contemplate those dhammas? … Thus one contemplates those dhammas.
'Development' (bhāvanā): there are four kinds of development … development in the sense of repeated practice. The out-breaths and in-breaths of one contemplating fading away are purification of virtue in the sense of restraint … For one who understands the one-pointedness and non-distraction of the mind by way of the out-breaths and in-breaths while contemplating fading away … understanding, one brings the faculties into unity. Therefore it is said: 'and one penetrates that which has peace as its meaning.'
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.