Śāṇḍilya Upaniṣad 1.1_3

1.1_3

athāsanadṛḍho yogī vaśī mitahitāśanaḥ suṣumnānāḍīsthamalaśoṣārthaṃ yogī baddhapadmāsano vāyuṃ candreṇāpūrya yathāśakti kumbhayitvā sūryeṇa recayitvā punaḥ sūryeṇāpūrya kumbhayitvā candreṇa virecya yayā tyajettayā sampūrya dhārayet |
tadete ślokā bhavanti |
prāṇaṃ prāgiḍayā pibenniyamitaṃ bhūyo'nyayā recayetpītvā piṅgalayā samīraṇamatho baddhvā tyajedvāmayā |
sūryācandramasoranena vidhinā'bhyāsaṃ sadā tanvatāṃ śuddhā nāḍigaṇā bhavanti yamināṃ māsatrayādūrdhvataḥ ||

"Then having become firm in the posture and preserved perfect self-control, the yogin should, in order to clear away the impurities of the Sushumnā, sit in the paḍmāsana (paḍma posture), and having inhaled the air through the left nostril, should retain it as long as he can and should exhale it through the right. Then drawing it again through the right and having retained it, he should exhale it through the left in the order that he should draw it through the same nostril by which he exhaled it before and retained it. In this context, occur (to memory) the following verses: "In the beginning having inhaled the breath (Prāṇa) through the left nostril, according to the rule, he should exhale it through the other; then having inhaled the air through the right nostril, should retain it and exhale it through the other." To those who practise according to these rules through the right and left nostrils, the nādis become purified within three months. He should practise cessation of breath at sunrise, in the midday, at sunset and at midnight slowly till eighty (times a day) for four weeks. In the early stages, perspiration is produced; in the middle stage the tremor of the body, and in the last stage levitation in the air. These (results) ensue out of the repression of the breath, while sitting in the paḍma posture. When perspiration arises with effort, he should rub his body well. By this, the body becomes firm and light. In the early course of his practice, food with milk and ghee is excellent. One sticking to this rule becomes firm in his practice and gets no ṭāpa (or burning sensation in the body). As lions, elephants and tigers are gradually tamed, so also the breath, when rightly managed (comes under control); else it kills the practitioner.