[1328] Bhikkhus, how is concentration (samādhi) by mindfulness of breathing (ānāpānasati) developed, how is it cultivated, so that it is of great fruit and great benefit? 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, having set his body erect, having established mindfulness in front of him. Just mindful he breathes in; mindful he breathes out. Breathing in long, he knows, "I breathe in long" … (to be expanded as far as: he trains thus, "Contemplating relinquishment I shall breathe in"; he trains thus, "Contemplating relinquishment I shall breathe out"). Developed thus, bhikkhus, cultivated thus, concentration by mindfulness of breathing is of great fruit and great benefit.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.