Mindfulness of Breathing
MN 118 Ānāpāna Sati Sutta: Mindfulness of Breathing
“There is the case where a monk, having gone to the wilderness, to the shade of a tree, or to an empty building, sits down folding his legs crosswise, holding his body erect, and setting mindfulness to the fore. Always mindful, he breathes in; mindful he breathes out.”