Mandukya Karika, verse 3.34-35
निगृहीतस्य मनसो निर्विकल्पस्य धीमतः ।
प्रचारः स तु विज्ञेयः सुषुप्तेऽन्यो न तत्समः ॥ ३४ ॥
nigṛhītasya manaso nirvikalpasya dhīmataḥ |
pracāraḥ sa tu vijñeyaḥ suṣupte'nyo na tatsamaḥ || 34 ||
34. The behaviour of the mind that is under control, i.e., which is free from all imaginations and that is endowed with discrimination, should be known. The condition of the mind in deep sleep is of another sort and not like that.
लीयते हि सुषुप्ते तन्निगृहीतं न लीयते ।
तदेव निर्भयं ब्रह्म ज्ञानलोकं समन्ततः ॥ ३५ ॥
līyate hi suṣupte tannigṛhītaṃ na līyate |
tadeva nirbhayaṃ brahma jñānalokaṃ samantataḥ || 35 ||
35. As the mind is withdrawn at the time of deep sleep and not so in the case of the (Vedāntic) discipline, (therefore there is a difference between the condition of the mind of a sleeper and that of a Jñāni). That (mind of a Jñāni) becomes identical with fearless Brahman whose all-round illumination is conciousness alone.
Shankara Bhashya (commentary)
It has been stated before that the mind, free from imagination on account of the knowledge1 of Truth, which is Ātman, becomes tranquil for want of external objects, like the fire not fed by fuel. Such mind may be said to be under control, It has been further stated that duality disappears when the mind thus ceases to act. The Yogis should particularly know the behaviour2 of the mind which is thus brought under discipline, which is free from all imaginations and which is possessed of discrimination. (Objection)—In3 the absence of all specific consciousness the mind, in the state of deep sleep, behaves exactly in the same manner as does the mind under control. What is there to be known in the absence of all specific knowledge? (Reply)—To this objection we reply thus:—Your objection is not valid. For, the behaviour of the mind in deep sleep, overcome by the darkness of delusion caused by ignorance, and still full of many potential desires which are the seeds of numerous future undesirable activities, is quite different from the behaviour of the mind well under control and free from the ignorance which produces activities that give rise to numerous afflictions, and from which has been burnt away by the fire of self-knowledge the ignorance which contains the harmful seed of all potential tendencies to act. The behaviour of the latter kind of mind is quite different.4 Therefore it is not like the mind in deep sleep. Hence the behaviour of such mind should be known. This5 is the purport. Now is stated the reason for the distinction between the behaviour (of the mind of a sleeper and that of a Jñāni). The mind in deep sleep, with the desires which are the cause of all experiences during the state of ignorance, goes1 back to the seed-like condition of potentiality characterised by the undifferentiated2 feature of darkness; but the3 mind (of a Jñāni) which is disciplined by discrimination is not so withdrawn, that is to say, does not go back to the seed-like state of darkness. Therefore is made the distinction between the behaviour of the mind in deep sleep and that of a Jñāni whose mind is under control. When the mind becomes free from all ideas of the perceiver and the perceived—the dual evils caused by ignorance—it verily becomes one with the Supreme and the non-dual Brahman. Therefore the mind becomes free from all fear; for, in that state, the perception of duality, which is the cause of fear, is absent. Brahman is peace and fearlessness. Having realised Brahman, the Jñāni is not afraid of anything. This is thus further amplified: Jñānam means the essence of Knowledge, i.e., the consciousness which is the very nature of Ātman or the Self. Brahman is that whose expression is the Knowledge thus described. In other words, Brahman is the one mass of sentiency. The word, “all-round” in the text, implies that this knowledge of Brahman is without4 break and all-pervading like the ether.