Maharishi Patanjali has defined Yoga as "the detention of the thoughts of the mind". In Yoga Sutra, he explained in detail the path of Yoga with eight limbs for full wellness and physical, mental and spiritual purification. Ashtang-Yoga is eight dimensional paths:
(Yoga Sutra 29 - यमनियमासनप्राणायामप्रत्याहारधारणाध्यानसमाधयोऽष्टाव अङ्गानि ॥) i.e. Yama, Niyama, Asana, Pranayama, Pratyahara, Dharna, Dhyana and Samadhi are eight limbs of yoga.
The Yama and Niyama are moral trainings; without Pratyâhâra, or restraint of the senses from their objects; Dhâranâ, or fixing the mind on a spot; Dhyâna, or meditation; and Samâdhi, or superconsciousness. The mind can exist on a still higher plane, the superconscious. The three — Dharana, Dhyana, and Samadhi — together, are called Samyama.
Ashtang Yoga impacts Panch Kosh. Yama, Niyama and Asana on Annmya Kosh, Pranayama on Pranamaya Kosh, Dharna & Dhyana on Manomaya Kosh & Vigyanmaya Kosh and Samadhi on Annandamaya Kosh.
Shree Krishna in Bhagavad Gita has explained the concepts of yogic ideals in its chapter 6 & 8 and stressed that one who abandon the body & mind while contemplating the Nirgun Brahma, that man achieves the eternal divine.
Eight limbs of Ashtang yoga and path shown by Shree Krishna are given hereunder:
I. Yama: Five Social Ethics – how to behave in External environment.
(Yoga Sutra 30 - अहिंसासत्यास्तेयब्रह्मचर्यापरिग्रहा यमाः ॥)
i.e. Ahimsa (Non-violence), Satya (Truthfulness), Asteya (Non-stealing), Brahmacharya (Chastity) and Aparigraha (Non-accumulating)
II. Nyama (Rule): Five Personal Ethics – how to behave with body & mind and to discipline them.
(Yoga Sutra 32 - शौचसंतोषतपःस्वाध्यायेश्वरप्रणिधानानि नियमाः ॥)
i.e. Shaucha (purity or cleanliness), Santosha (contentment), Tapas (austerity), Svâdhyâya (study) and Ishvara-pranidhâna (worshipping and self-surrender God).
III.Asana : Body postures or Yogasons to make body & mind stable, tranquil and healthy.
IV.Pranayama : Prana means the vital forces in one's own body, Âyâma means controlling them.
It is control of life force by breathing techniques. First, it purifies the nerves. Shankaracharaya in his commentary on the Shvetâshvatara Upanishad quoted: "The mind, whose dross has been cleared away by Pranayama, becomes fixed in Brahman.
[Stopping the right nostril with the thumb, through the left nostril fill in air, according to capacity; then, without any interval, throw the air out through the right nostril, closing the left one. Again inhaling through the right nostril eject through the left.]
V.Pratyahara (Withdrawal): means, "gathering towards," checking the outgoing powers of the mind, freeing it from the control of the senses.
One who has succeeded in attaching or detaching his mind to or from the centres at will.
The human mind is like that monkey, incessantly active by its own nature. If one can restrain the mind-stuff or chitta and keep it calm, this is called Pratyahara. One should simply watch the thoughts. Gradually, these will subsidise.
VI. Dharna (Perception): To make mind stable and being concentrated
To hold the mind on certain part of the body to the exclusion of others
VII.Dhayan (Meditation): constant meditation.
When one has so intensified the power of Dhyana as to be able to reject the external part of perception and remain meditating only on the internal part, the meaning, that state is called Samadhi. Only one wave is left in the mind.
We have, then, two planes in which the human mind works. First is the conscious plane, in which all work is always accompanied with the feeling of egoism. Next comes the unconscious plane, where all work is unaccompanied by the feeling of egoism. There is a still higher plane upon which the mind can work i.e. above consciousness. It is called Samâdhi or superconsciousness. Unconscious, conscious, and superconscious states — belong to one and the same mind. There are not three minds in one man, but one state of it develops into the others.
When a man goes into deep sleep, he enters a plane beneath consciousness. He works the body all the time, he breathes, he moves the body, perhaps, in his sleep, without any accompanying feeling of ego; he is unconscious, and when he returns from his sleep, he is the same man who went into it. The sum total of the knowledge which he had before he went into the sleep remains the same; it does not increase at all. No enlightenment comes.
VIII.Samadhi (Kavaliya): Perfect concentration, Connecting to the soul: beyond the words, limits of reason, state of trance.
When mind itself is the object of meditation. If the mind can be fixed on the centre for twelve seconds it will be a Dharana, twelve such Dharanas will be a Dhyana, and twelve such Dhyanas will be a Samadhi.
In Samadhi, all the tendencies which become waves are eliminated.
Sri Krishna in Bhagavad Gita has explained the concepts of yogic ideals in chapter 6 & 8 as under:
Aspirant (Yogi) to withdraw and hold mind and senses, sit in solitary place and put attention of soul into eternal divine.
By sitting in that seat, keeping the mind and actions of the senses under control, practice yoga for purification of interaction by integrating the mind.
He should keep body, head and neck stable and look at the face of the nostrils without looking at other directions.
Yogi who keeps check on mind and continuously put soul in eternal divine, gets the ultimate peace of ecstasy.
Such Yogi who has been practicing effortlessly, is completely free from all sins of past many lives in this life only and attains Paramagti (no rebirth takes place).
Yogi, who establishes attention between eyebrows and remembers the eternal divine with great devotion & stable mind, reaches to eternal divine only.
Yogi who by blocking the gates of all the senses, with stable mind, put attention of eternal divine on forehead and continuously repeats “Aum”, he achieves eternal divine. (i.e. abandon the body & mind while contemplating the Nirgun Brahma, that man achieves the eternal divine).