Section of Satipatthana Sutta referred to:
"A practitioner goes do the forest or to the root of a tree or to an empty hut, sits down; having folded the legs crosswise, sits with body erect, and with mindfulness established to the forefront; every mindful one breathes in, mindful one breathes out.
Breathing in long, one knows, "I breathe in long."
Breathing in short, one knows, "I breathe in short."