“Mendicants, when immersion due to mindfulness of breathing is developed and cultivated it leads to the ending of defilements. “… Āsavānaṁ khayāya saṁvattati. And how is immersion due to mindfulness of breathing developed and cultivated so as to lead to giving up the fetters, Kathaṁ bhāvito ca, bhikkhave, ānāpānassatisamādhi kathaṁ bahulīkato saṁyojanappahānāya saṁvattati … uprooting the underlying tendencies, anusayasamugghātāya saṁvattati … completely understanding the course of time, addhānapariññāya saṁvattati … and ending the defilements? āsavānaṁ khayāya saṁvattati?

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 front of them. … Idha, bhikkhave, bhikkhu araññagato vā rukkhamūlagato vā …pe…

They practice like this: ‘I’ll breathe in observing letting go.’ They practice like this: ‘I’ll breathe out observing letting go.’ paṭinissaggānupassī assasissāmīti sikkhati, paṭinissaggānupassī passasissāmīti sikkhati.

That’s how immersion due to mindfulness of breathing is developed and cultivated so as to lead to giving up the fetters, Evaṁ bhāvito kho, bhikkhave, ānāpānassatisamādhi evaṁ bahulīkato saṁyojanappahānāya saṁvattati …pe… uprooting the underlying tendencies, anusayasamugghātāya saṁvattati …pe… completely understanding the course of time, addhānapariññāya saṁvattati …pe… and ending the defilements.” āsavānaṁ khayāya saṁvattatī”ti.

Dasamaṁ.

Dutiyo vaggo.

Tassuddānaṁ

Icchānaṅgalaṁ kaṅkheyyaṁ, ānandā apare duve; Bhikkhū saṁyojanānusayā, addhānaṁ āsavakkhayanti.

The Linked Discourses on Mindfulness of Breathing is the tenth section. Ānāpānasaṁyuttaṁ dasamaṁ.