Vijnana Bhairava Tantra · Dharana 4 · Verse 27
Spontaneous retention
Do not force the breath to stop. After some time sitting, it may pause on its own at the end of an inhalation or an exhalation. If it does, remain in the pause. The verse also covers deliberate holding of the breath; this desk teaches only the gentle, spontaneous form, because forced retention is best learned from a teacher. This practice is simply not restarting what has already gone still.
Older line
When the breath comes to rest, held after the out-breath or after the in-breath, then at the end of that resting, through the power called Peace, the Peaceful One shines forth.