Vijnana Bhairava Tantra · Dharana 32 · Verse 55
Breath, dense and fine
Sense the energy of the breath as dense and full in the heart, and thin and fine at the far point where the out-breath ends, about twelve finger-widths beyond the body. Let attention move between the two, then enter the heart and rest there. The old text says this practice brings a new freedom, even within dreams.
Older line
Meditating on the life-energy as dense in the heart and subtle at the far end of the breath, and entering into it there, one becomes free, even in dreams.