idha, bhikkhave, bhikkhu ara~n~nagato vaa rukkhamuulagato vaa su~n~naagaaragato vaa nisiidati, palla"nka.m aabhujitvaa, uju.m kaaya.m pa.nidhaaya, parimukha.m sati.m upa.t.thapetvaa. so satova assasati, sato passasati.
Here, o bhikkhus, a bhikkhu* gone to the forest, gone to the root of a tree, or gone to an empty dwelling, sits with his legs crossed and body straight, keeping remembrance of the present moment at the fore. Thus he breathes in with remembrance; thus he breathes out with remembrance.
-- The Buddha
* bhikkhu = one who sees (ikkhati) the danger (bhaya) of old age, sickness and death, and cuts off (bhindati) the corruptions (kilesa) that exist in one's own heart.