Bhagavad Gita: The Practice of Yoga

"A yogi should always concentrate his mind on the Supreme self in a lonely place all by himself. Such a person will have certainly won over his mind, senses, and body and will be free from all desires and possessions.

In a clean place with kusa grass, a deerskin, and a pure cloth placed one above the other, one should not raise the seat too high nor too low and thus being situated on the seat, concentrating the mind, one must control the thoughts and actions of the senses and must practice yoga for the purification of the self.

Keeping the body, head, and neck straight and steady with firmness and looking only at the tip of his nose without seeing elsewhere. Situated in the vow of Brahmacharya (free from sex life), being fearless, calm and vigilant in mind and having subdued the mind, one should fix it (mind) on Me [Lord Krishna] thinking of Me as the Supreme Goal in life.

In this way, constantly engaging the mind in the form of the Lord, the yogi of subdued mind, attains the Supreme eternal peace residing in Me.

O Arjuna! Yoga is not for him who eats too much nor for him who does not eat at all. And not for him who sleeps very much nor for him who is always awake.

Only one who takes limited (suitable) food, limited recreation, performs suitable actions, regulates sleep and wakes up suitably and accordingly, attains yoga — which is the destroyer of all sorrows.

When such a perfectly controlled mind gets fully situated in the Lord, then, at that time, free from desires of all sense gratifications, such a person is considered to be well established in yoga.

Just as a lamp placed in an airless place does not flicker, similarly it is said of the minds of the yogis situated in the meditation of God that they also do not flicker.

When the mind, subdued by the practice of yoga comes to rest, and when the pure intellect realizes the Lord, it becomes satisfied in the Lord itself. And when one enjoys the Supreme eternal bliss that is beyond the perception of senses and obtainable only through the intelligence, a yogi situated in such a condition never deviates from the Supreme self. And having gained such a condition he does not consider anything as more profitable than this. And a Yogi situated in such a position is never afflicted even by the greatest sorrow. That which is away from the union of painful world is called Yoga and must be clearly known. And such yoga must be decisively practiced by the constant, undisturbed mind. This stage of perfection is called trance (Samadhi)."

— The Bhagavad Gita, Chapter 6, Verse 6-23