What is Yoga, as per the Svetasvatara Upanishand
II-7: Attaining whom thou destroyest the source and art no more troubled by the results of past actions – to that ancient Brahman be thou devoted through the Prime Cause, the Immanent Soul.
II-8: Placing the body in a straight posture, holding the chest, throat and head erect, and drawing the senses and the mind into the heart, the knowing one should cross over all the fearful currents by means of the raft of Brahman.
II-9: Controlling the senses with an effort, and regulating the activities in the body, one should breathe out through the nostrils when the vital activities become gentle. Then the knowing one, without being in the least distracted, should keep his hold on the mind as on the reins attached to restive horses.
II-10: One should perform one’s exercises in concentration, resorting to caves and such other pure places helpful to its practice – places where the ground is level without pebbles, and the scenery pleasing to the eyes; where there is no wind, dust, fire, dampness and disturbing noises.
II-11: Forms that appear like snow, smoke, sun, wind, fire, fire-fly, lightning, crystal and moon, precede the manifestation of Brahman in Yoga practice.
II-12: When the fivefold perception of Yoga, arising from (concentrating the mind on) earth, water, light, air and ether, have appeared to the Yogin, then he has become possessed of a body made of the fire of Yoga, and he will not be touched by disease, old age or death.
II-13: It is said that the first signs of entering Yoga are lightness of body, health, thirstlessness of mind, clearness of complexion, a beautiful voice, an agreeable odour and scantiness excretions.
II-14: Just as the same metal disc, which was stained by dust before, shines brilliantly when cleaned, so the embodied being, seeing the truth of Atman, realizes oneness, attains the goal and becomes sorrow-less.
II-15: When the Yogin realizes the truth of Brahman, through the perception of the truth of Atman in this body as a self-luminous entity, then, knowing the Divinity as unborn, eternal and free from all the modifications of Prakriti, he is freed from all sins.