Hathayoga 1-50

कृत्वा सम्पुटितौ करौ दृढतरं बद्ध्वा तु पद्ममासनं
गाढं वक्षसि सन्निधाय चिबुकं ध्यायंश्च तच्चेतसि ।
वारं वारमपानमूर्ध्वमनिलं प्रोत्सारयन्पूरितं
न्यञ्चन्प्राणमुपैति बोधमतुलं शक्ति-प्रभावान्नरः ॥ ५०॥

Krtvā samputitau karau drdhataram Baddhvā tu padmamāsanam
Ghādham vakshasi sannidhāya chibukam Dhyāyamścha tachchetasi
Vāram vāramapānamūrdhvamanilam Protsārayanpūritam
Nyañchanprānamupaiti bodhamatulam śaktiprabhāvānnarah

Having kept both the hands together in the lap, performing the Padmâsana firmly, keeping the chin Fixed to the chest and contemplating on Him in the mind, by drawing the apânavâyû up (performing mûla Bandha) and pushing down the air after inhaling it, joining thus the prâna and apâna in the navel, one gets the highest intelligence by awakening the śakti (kundalinî) thus.

N.B.:- When Apâna Vâyû is drawn gently up and after filling in the lungs with the air from outside, the prâna is forced down by and by so as to join both of them in the navel, they both enter then the Kundalinî and, reaching the Brahma randhra (the great hole), they make the mind calm. Then the mind can contemplate on the nature of the âtmana and can enjoy the highest bliss.