There are so many verses both in the Upanishads and in Shankara’s commentaries which state that all thoughts must be extinguished for liberation to occur. Here are some of these verses (and there are many many more!):
(Note I have not included the numerous verses from Shankara’s text called Vivekachudamani which repeatedly advocates the thoughtless state of Nirvikalpa Samadhi which can be found in a separate post here)
When the five organs of perception become still, together with the mind, and the intellect ceases to be active: that is called the Supreme State [Brahma-Vidya or Self Knowledge]
~Katha Upanishad 2.3.10
Shankara’s commentary on this above verse (Katha Upanishad, verse 2.3.10) states the following:
‘At the time when the five senses…, together with the mind…, which is now no longer functioning and thinking, are at rest in the Self alone, after turning away from objects, and with the intellect…no longer engaging with its functioning, that they call the highest state [Brahma-Vidya or Self-Knowledge].’
This is reminiscent of the Amritabindu Upanishad and also of the Adhyatma Upanishad, both of which are considered to be traditional Upanishads in the Advaita Vedanta/ Jnana tradition:
The mind severed from all connection with sensual objects, and prevented from functioning out, awakes into the light of the heart, and finds the highest condition. The mind should be prevented from functioning, until it dissolves itself in the heart. This is Jnana, this is Dhyana, the rest is all mere concoction of untruth.
~ Amritabindu Upanishad
The knot of the ignorance in the heart is broken completely only when one sees his Self as secondless through Nirvikalpa Samadhi
~Adhyatama Upanishad 1.17
Gaudapada writes in verse 3.38 of his Mandukya Karika:
There can be no acceptance or rejection where all mentation stops. Then knowledge is established in the Self and is unborn, and it becomes homogenous
Shankara’s commentary on this verse 3.38 is as follows:
…therefore there is no rejection or acceptance in It, where thought does not exist. That is to say, how can there be rejection or acceptance where no mentation is possible in the absence of the mind? As soon as there comes the realisation of the Truth that is the Self, then, in the absence of any object, knowledge (Jnanam) is established in the Self, like the heat of fire in fire. It is then birthless (ajati) and becomes homogenous.
‘…when the mind becomes quiescent and does not give rise to appearances, it verily becomes Brahman’
~ Gaudapada, Mandukya Upanishad Karika 3.46
Shankara clarifies this further in his commentary on Mandukya Karika 3.46:
‘When the mind brought under discipline by the above-mentioned methods, does not fall into the oblivion of deep sleep, nor is distracted by external objects, that is to say, when the mind becomes quiescent like the flame of a light kept in a windless place; or when the mind does not appear in the form of an object – when the mind is endowed with these characteristics, it verily becomes one with Brahman.’
Anandagiri, a 13th century commentator on Shankara’s works, confirms this in his comments on Karika 3.46:
‘The external objects are nothing but the activities of the mind itself.’
So we can see that mind activity and external objects are one and the same, and that samadhi is devoid of both
The knowers of Brahman say that absolute Jnanam, knowledge, which is akalpakam [devoid of thoughts], and is therefore ajam, birthless…
~ Shankara’s commentary on Gaudapada Karika 3.33
This duality as a whole, that is mano-drsyam, perceived by the mind; is nothing but the mind, which is itself imagined – this is the proposition [Tom: ie. meaning of the verse]. For duality endures so long as the mind does, and disappears with the disappearance of the mind.
~ Shankara’s commentary on Gaudapada Karika 3.31
It has been said that when the mind is divested of ideation by virtue of the realisation of Truth that is Brahman, and when there is an absence of external objects (of perception), it becomes tranquil, controlled, and withdrawn, like fire that has no fuel. And it has further been said that when the mind thus ceases to be mind, duality also disappears.
~ Shankara’s commentary on Gaudapada Karika 3.33
‘The controlled mind is verily the fearless Brahman’
~Gaudapada Karika 3.35
On p.149 of The Method of Vedanta by SSS, SSS quotes from Chapter 6 of the Bhagavad Gita to explain in more detail the method of Nididhyasana, as follows:
‘That yoga should certainly be practised with resolute mind. Giving up without exception all desires that come from individual, will, restraining the sense-organs on every side through the mind, one should gradually withdraw from all activity, with will and intellect firmly controlled; keeping the mind fixed on the Self, one should not think of anything. Wherever the fickle mind wanders, one should bring it back and fix it on the Self alone, under firm control. Supreme joy comes to such a yogi, whose mind is at perfect peace, whose lusts have subsided, who is sinless and who has become the Absolute.’
I thought I would end with Bhagavan Sri Ramana Maharshi’s view of the scriptures and their purpose:
All the jnana scriptures that teach the way to redemption proclaim in unison that restraining and stilling the mind is the best means for liberation. This is also emphasised by jnanis. If, after a certain amount of study, one knows this to be the inner purport of the scriptures, one should then direct ones whole effort towards that [practice]. What is the use of continuously studying more and more scriptures without doing this?
~Sri Ramana Maharshi, Guru Vachaka Kovai verse 141