Devibhagavatapurana 7.35.11

7.35.11

jānūrvorantare samyakkṛtvā pādatale śubhe |
ṛjukāyo viśedyogī svastikaṃ tatpracakṣate ||

Place the soles of the feet completely under the thighs, keep the body straight, and sit at ease. This is called the Svastikâsan. Bhadrâsan consists in placing well the two heels on the two sides of the two nerves of the testicle, near the anus and catching by the two hands the two heels at the lower part of the testicles and then sitting at ease. This is very much liked by the Yogis. Vajrâsan (diamond seat) consists in placing the feet on the two thighs respectively and placing the fingers below the thighs with the hands also there, and then sitting at ease. Vîrasan consists in sitting cross on the hams in placing the right foot under the right thigh and the left foot under the left thigh and sitting at ease with body straight.
Taking in the breath by the Idâ (the left nostril) so long as we count "Om" sixteen, retaining it in the Susumnâ so long as we count "Om" sixty-four times and then exhaling it slowly by the Pingalâ nâdi (the right nostril) as long as we count "Om" thirty-two times. (The first process is called Pûraka, the second is called Kumbhaka, and the third is called Rechaka). This is called one Prânâyâma by those versed in the Yogas. Thus one should go on again and again with his Prânâyâma. At the very beginning, try with the number twelve, i. e., as we count "Om" twelve times and then increase the number gradually to sixteen and so on. Prânâyâma is of two kinds:-- Sagarbha and Vigarbha. It is called Sagarbha when Prânâyâma is performed with repeating the Ista Mantra and Japam and meditation. It is called Vigarbha Prânâyâma when "Om" is simply counted and no other Mantram. When this Prânâyâma is practised repeatedly, perspiration comes first when it is called of the lowest order; when the body begins to tremble, it is called middling; and when one rises up in the air, leaving the ground, it is called the best Prânâyâma. (Therefore one who practises Prânâyâma ought to continue it till he becomes able to rise in the air).