The Breath for the Enlightenment - Ekadhamma Sutta

​Namo  Tassa  Bhagavato  Arahato  Samma  Sambuddhassa !

Homage to the Blessed One, the Worthy One, the Supremely Enlightened One !
Ekadhamma Sutta - The Discourse on One Thing.So I have heard. At one time the Buddha was staying near Sāvatthī in Jeta’s Grove, Anathapindika’s monastery. There the Buddha addressed the monks:  “Mendicants ! ” -  “ Venerable sir, ” they replied. The Buddha said this:  “Mendicants, when one thing is developed and cultivated it’s very fruitful and beneficial. What one thing ? Mindfulness of breathing. And how is mindfulness of breathing developed and cultivated to be very fruitful and beneficial ? 

( 1 )  It’s when a mendicant has gone to a wilderness, or to the root of a tree, or to an empty hut. They sit down cross-legged, with their body straight, and establish mindfulness right there. 
( 2 )  Just mindful, they breathe in. Mindful, they breathe out.( 3 ) When breathing in heavily they know: ‘I’m breathing in heavily.’ When breathing out heavily they know: ‘I’m breathing out heavily.’ 
( 4 )  When breathing in lightly they know: ‘I’m breathing in lightly.’ When breathing out lightly they know: ‘I’m breathing out lightly.’ 
( 5 )  They practice like this: ‘I’ll breathe in experiencing the whole body.’ They practice like this: ‘I’ll breathe out experiencing the whole body.’ 
( 6 )  They practice like this: ‘I’ll breathe in stilling physical processes.’ They practice like this: ‘I’ll breathe out stilling physical processes.’
( 7 )  They practice like this: ‘I’ll breathe in experiencing rapture.’ They practice like this: ‘I’ll breathe out experiencing rapture.’ 
( 8 )  They practice like this: ‘I’ll breathe in experiencing bliss.’ They practice like this: ‘I’ll breathe out experiencing bliss.’         
( 9 )  They practice like this: ‘I’ll breathe in experiencing mental processes.’ They practice like this: ‘I’ll breathe out experiencing mental processes.’ 
( 10 ) They practice like this: ‘I’ll breathe in stilling mental processes.’ They practice like this: ‘I’ll breathe out stilling mental processes.’
( 11 ) They practice like this: ‘I’ll breathe in experiencing the mind.’ They practice like this: ‘I’ll breathe out experiencing the mind.’ 
( 12 ) They practice like this: ‘I’ll breathe in gladdening the mind.’ They practice like this: ‘I’ll breathe out gladdening the mind.’ 
( 13 )   They p ractice like this: ‘I’ll breathe in immersing the mind in samādhi.’ ( concentration )  They practice like this: ‘I’ll breathe out immersing the mind in samādhi.’ 
( 14 )  They practice like this: ‘I’ll breathe in freeing the mind.’ They practice like this: ‘I’ll breathe out freeing the mind.’ 
( 15 )   They practice like this: ‘I’ll breathe in observing impermanence.’ They practice like this: ‘I’ll breathe out observing impermanence.’
( 16 )   They practice like this: ‘I’ll breathe in observing fading away.’ They practice like this: ‘I’ll breathe out observing fading away.’ 
( 17 )   They practice like this: ‘I’ll breathe in observing cessation.’ They practice like this: ‘I’ll breathe out observing cessation.’ 
( 18 )   They practice like this: ‘I’ll breathe in observing letting go.’ They practice like this: ‘I’ll breathe out observing letting go.’
Mindfulness of breathing, when developed and cultivated in this way, is very fruitful and beneficial.”
Sādhu ! Sādhu !! Sādhu !!!  ( Excellent )

Reference : https://suttacentral.net/sn12.1/en/sujato - Translated by Bhikkhu Sujato.