Yōga Sūtra 2.50

बाह्याभ्यन्तरस्तम्भवृत्तिः देशकालसङ्ख्याभिः परिदृष्टो दीर्घसूक्ष्मः।

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