Yōga Sūtra 2.50

bāhyābhyantarastambhavr̥ttiḥ dēśakālasaṅkhyābhiḥ paridr̥ṣṭō dīrghasūkṣmaḥ।

The acts of suspending air outside or inside must be regulated based on place, time, and counts, making it prolonged and subtle.