[1312] And how, bhikkhus, is mindfulness of breathing (ānāpānasati) developed, how is it cultivated much, so that it is of great fruit and great benefit? Here, bhikkhus, a bhikkhu, gone to the forest, or gone to the foot 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. (To be expanded in full, as far as: he trains thus, "Contemplating relinquishment (paṭinissagga), I shall breathe in"; he trains thus, "Contemplating relinquishment, I shall breathe out.") It is when mindfulness of breathing is developed thus, bhikkhus, and cultivated much thus, that it is of great fruit and great benefit.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.