Manduka Upanishad:~ Samadhi and sleep are identical.+

Sage Sankara says: ~ "There is no need to indulge in yoga, to realize the ultimate truth or Brahman

Sage Sankara says the transparent Truth of the Self, which is hidden by the illusion, is to be attained through the instructions of a knower of Brahman, (Gnani)

Sage Sankara says: ~ “The exercise in discrimination between real and unreal and renunciation of the false is real meditation, then why you are indulging in other types of meditation.

Yoga has its place rather than its value and its value is for a certain type of mindset. Yoga will remove restlessness, and helps to get receptiveness, but never Truth because it ignores the external world. Yoga cannot remove ignorance. It is only a step. It removes obstructions.

Yoga can yield only the duality because everything that one can do or practice becomes a vanishing 'known.' It yields the relative truth, i.e. true from a particular viewpoint, not the ultimate truth.

Yoga implies duality! Yoga means joining two things, something to which the yogi is to be joined. He thinks I want to know God, I want to attain Union. So he has the ego and cannot attain, whereas the first thing in the path of truth is to question the ‘I’ until its illusory nature is perceived and the seeker no longer says "I want to attain ultimate truth.

One has nothing to get for the self, as it has vanished on inquiry, not even will he say I will work for the sake the humanity.

In Sutra Bashya and Manduka Upanishad:~  Samadhi and sleep are identical. 

Brihad Upanishad does not advocate Samadhi.

It is not possible to stop the thought for more than a half-second whilst in the waking experience. If one succeeds in controlling thought and then banishes it, one passes into Nirvikalpa Samadhi, which is identical to deep sleep. The only difference between ordinary deep sleep and Samadhi, therefore, is that the ordinary man falls asleep involuntarily whereas the yogi has the satisfaction of knowing that he has passed into sleep by his own effort of will in banishing thoughts.

Sage Patanjali warns against sleep as a hindrance to yoga, he means when it occurs in the early stages of the practice before one has obtained the power of control and consequently banishes the thought. The fact that Samadhi is deep sleep is kept secret because people would not be tempted to take up yoga. Then what is its value of it? Why, to sharpen the mind, to enable it to keep away all extraneous thoughts when one gets out to reason in the practice of the next higher stage, i.e. Gnana.

 Yoga is thus simply a sharpening stone for the mind to enable it to take up Gnana. Living without thoughts is Impossible. The very thoughtless state itself is a thought.  Holding the thoughtless thought and entering the Samadhi is impossible without the thought of thoughtlessness. How can one enter the Samadhi without the thought of thoughtlessness?   He does not know the Gnanic truth if he says thoughtlessness is the perfect stage of the  Self.

When thoughts are stilled, it is not the Self that is found. It is only the mind. Thus,  Yogic Samadhi is not Gnana and therefore yogi does not know the Advaita the highest truth. Yoga is good to give peace and concentration, but only to start reasoning, i.e. thinking again to find the truth.

Yogic Samadhi is not the goal,  but a means to an end, i.e. Gnana. Samadhi in itself is useless because the mind is withdrawn and there is no memory of it until after it is over and one returns to waking experience.  Yogi who attains Samadhi: it is only the sleep.

Yogi who is said to experience non-duality in his ecstasy must still come back to a normal state and see the world confronts him, after his ecstasy. And then he will find that the world separates from him because he has ignored it and not tried to understand it. Only the Gnani can say of the external world, "This is Brahman, Soul." and prove his statement, and that it is none other than the innermost Self.

Many yogis are largely pretenders or self-deluded. They think they are masters who can lead the whole of humanity. They set themselves up as different from others. Many yogis promise blessings etc. to those who surrender their wealth or person to them. Many here live questionable lives with women disciples.  They seek influence over others, or wealth, by thus differentiating themselves.  They market their yogic products in the spiritual supermarket.  A Gnani never does this.

If a yogi says "I feel Bliss" who is having the experience? His 'I' is the ego. Hence,  that is not the highest Gnana.  If one carefully examines the experiences of mystics, then he finds that they do differ. It is superficial to say that yogis and mystics all have the same experience.

In the dream one knows that the dream figures are also minded, not different from it; similarly, when one knows that everything is consciousness, there is no need for the yogic control of the mind. Control presupposes second, a duality. Hence, yoga is in the sphere of duality and is unnecessary to one who knows non-duality.

Remember:~ 

Self-Knowledge requires the mind to be active to examine the world and discriminate. Hence nondual wisdom means knowing that there are no ideas different from the innermost self, which is in the form of consciousness, as the dream mountain is not different from Mind, knowing which they automatically the mind reaches stillness. This is different from Yogic Samadhi, which is only a deep sleep.

The Yogis and Mystics want meditation, sitting still, etc. only because it gives them pleasure: the satisfaction is for their own selves only, not others; hence it is something sought by the ego and cannot get the ultimate truth or Brahman in consequence.

The Yogi wants to do something, some action, even that of sitting still, to control this or concentrate on that. This means he is still attached to his physical body. He wants his physical body to be quiet. He is still thinking of an illusory physical body. He does not know that the physical body is part of the mirage. On the contrary, he takes it for reality.

The world must be seen before one can know its true nature in Gnana. The yogi, who shuts it out, thereby deprives himself of the opportunity to achieve Gnana.

The yogi must go to the ashram, some special place, some cave, or other. Whoever must sit in a posture is attached to the body.

The inquiry must begin with duality, i.e. with the world to inquire into. It will end with unity. The Yogi tries to avoid this duality by ignoring the universe. Hence,  he gets a false unity only.

The seekers of truth will inquire and practice discrimination.  The ultimate truth has to be attained not by intuition but by reason, which is superior to it. Not even a combination of intellect and intuition will find the truth, which is beyond form, time, and space.

Yoga will only let one know what he imagines. Self-Knowledge is the sum of all sciences. Scientists think only of the external world, the seekers of truth the inner self. Both are needed. Answers to prayers are imagination, due to chance.  Religion and Yoga are useful from utilitarian viewpoints, but from the standpoint of seeking the truth, they are useless. Yoga belief is a self-mesmeric condition out of which it is extremely difficult to escape.:~Santthosh Kumaar