“Mendicants, when mindfulness of breathing is developed and cultivated it’s very fruitful and beneficial. “Ānāpānassati, bhikkhave, bhāvitā bahulīkatā mahapphalā hoti mahānisaṁsā. And how is mindfulness of breathing developed and cultivated to be very fruitful and beneficial? Kathaṁ bhāvitā ca, bhikkhave, ānāpānassati kathaṁ bahulīkatā mahapphalā hoti mahānisaṁsā?

It’s when a mendicant—gone to a wilderness, or to the root of a tree, or to an empty hut—sits down cross-legged, sets their body straight, and establishes mindfulness in their presence. Idha, bhikkhave, bhikkhu araññagato vā rukkhamūlagato vā suññāgāragato vā nisīdati pallaṅkaṁ ābhujitvā ujuṁ kāyaṁ paṇidhāya parimukhaṁ satiṁ upaṭṭhapetvā.

Just mindful, they breathe in. Mindful, they breathe out. … So satova assasati, satova passasati …pe…

They practice like this: ‘I’ll breathe in observing letting go.’ They practice like this: ‘I’ll breathe out observing letting go.’ ‘paṭinissaggānupassī assasissāmī’ti sikkhati, ‘paṭinissaggānupassī passasissāmī’ti sikkhati.

Mindfulness of breathing, when developed and cultivated in this way, is very fruitful and beneficial. Evaṁ bhāvitā kho, bhikkhave, ānāpānassati evaṁ bahulīkatā mahapphalā hoti mahānisaṁsā. When mindfulness of breathing is developed and cultivated in this way you can expect one of two results: Evaṁ bhāvitāya kho, bhikkhave, ānāpānassatiyā evaṁ bahulīkatāya dvinnaṁ phalānaṁ aññataraṁ phalaṁ pāṭikaṅkhaṁ—enlightenment in this very life, or if there’s something left over, non-return.” diṭṭheva dhamme aññā, sati vā upādisese anāgāmitā”ti.

Catutthaṁ.