Vijnana Bhairava Tantra · Dharana 1 · Verse 24
Origins of the breath
Sit quietly. Notice that the breath is born twice: once where it turns and begins to come in, and once where it turns and begins to go out. Do not follow the whole stream. Rest attention at those two points of origin. Given nothing else to ride, the mind begins to settle into the stillness the breath keeps revealing.
Older line
The supreme power, whose nature is to pour forth, sounds without ceasing: the out-breath rising, the in-breath descending. Fill with awareness the two places where each is born, and you rest in fullness.