The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
54. There is separation (of the Self from the
body) because its existence does not depend on the existence of that (viz. the body), but there is not (non-separation); as in the case of perceptive consciousness.
The assertion that the Self is not separate from the body cannot be maintained. The Self rather must be something separate from the body, 'because the existence (of the Self) does not depend on the existence of that (i.e. the body).' For if from the circumstance that they are where the body is you conclude that the qualities of the Self are qualities of the body, you also must conclude from the fact that they are not where the body is that they are not qualities of the body, because thereby they show themselves to be different in character from the qualities of the body. Now the (real) qualities of the body, such as form and so on, may be viewed as existing as long as the body exists; life, movement, &c., on the other hand, do not exist even when the body exists, viz. in the state of death. The qualities of the body, again, such as form and so on, are perceived by others; not so the qualities of the Self, such as consciousness, remembrance, and so on. Moreover, we can indeed ascertain the presence of those latter qualities as long as the body exists in the state of life, but we cannot ascertain their non-existence when the body does not exist; for it is possible that even after this body has died the qualities of the Self should continue to exist by passing over into another body. The opposite opinion is thus precluded also for the reason of its being a mere hypothesis.--We further must question our opponent as to the nature of that consciousness which he assumes to spring from the elements; for the materialists do not admit the existence of anything but the four elements. Should he say that consciousness is the perception of the elements and what springs from the elements, we remark that in that case the elements and their products are objects of consciousness and that hence the latter cannot be a quality of them, as it is contradictory that anything should act on itself. Fire is hot indeed but does not burn itself, and the acrobat, well
trained as he may be, cannot mount on his own shoulders. As little could consciousness, if it were a mere quality of the elements and their products, render them objects of itself. For form and other (undoubted) qualities do not make their own colour or the colour of something else their objects; the elements and their products, on the other hand, whether external or belonging to the Self (the organism) are rendered objects by consciousness. Hence in the same way as we admit the existence of that perceptive consciousness which has the material elements and their products for its objects, we also must admit the separateness of that consciousness from the elements. And as consciousness constitutes the character of our Self, the Self must be distinct from the body. That consciousness is permanent, follows from the uniformity of its character (and we therefore may conclude that the conscious Self is permanent also; as also follows) from the fact that the Self, although connected with a different state, recognises itself as the conscious agent--a recognition expressed in judgments such as 'I saw this,'--and from the fact of remembrance and so on being possible 1.
The argumentation that consciousness is an attribute of the body because it is where a body is, is already refuted by the reasons stated above. Moreover, perceptive consciousness takes place where there are certain auxiliaries such as lamps and the like, and does not take place where those are absent, without its following therefrom that perception is an attribute of the lamp or the like. Analogously
the fact that perception takes place where there is a body, and does not take place where there is none, does not imply that it is an attribute of the body; for like lamps and so on the body may be used (by the Self) as a mere auxiliary. Nor is it even true that the body is absolutely required as an auxiliary of perception; for in the state of dream we have manifold perceptions while the body lies motionless.--The view of the Self being something separate from the body is therefore free from all objections.
271:1 The 'nityatvam ka' of the text might perhaps be connected directly with 'âtmano.' Ânanda Giri on the entire passage: Bhavatu tarhi bhûtebhyoऽtiriktâ svâtantryopalabdhis tathâpi katham âtmasiddhis tatrâha upalabdhîti, kshanikatvât tasyâ nityâtmarûpatvam ayuktam ity âsaṅkyâgânatas tadbhedâbhâvâd vishayoparâgât tadbhânâd asâv eva nityopalabdhir ity âha nityatvam keti, kim ka sthûladehâbhimânahînasya svapne pratyabhigñânâd atiriktâtmasiddhir ity âha aham iti, svapne sthûladehântarasyaivopalabdhritvam ity âsaṅkyâha smrityâditi, upalabdhrismartror bhede saty anyopalabdheऽnyasya smritir ikkhâdayas ka neti na tayor anyatety arthah.