The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
4. Not in the symbol (is the Self to be contemplated); for he (the meditating person) (may) not (view symbols as being the Self).
'Let a man meditate on mind as Brahman; this is said with reference to the body. Let a man meditate on ether as Brahman; this is said with reference to the Devas' (Kh. Up. III, 18, 1); 'Âditya is Brahman, this is the doctrine'
[paragraph continues] (Kh. Up. III, 19, 1); 'He who meditates on name as Brahman' (Kh. Up. VII, 1, 5). With regard to these and similar meditations on symbols a doubt arises whether the Self is to be apprehended in them also, or not.
The pûrvapakshin maintains that it is right to apprehend the Self in them also because Brahman is known from scriptural passages as the (universal) Self. For those symbols also are of the nature of Brahman in so far as they are effects of it, and therefore are of the nature of the Self as well.
We must not, our reply runs, attach to symbols the idea of Brahman. For he, i.e. the meditating person, cannot comprehend the heterogeneous symbols as being of the nature of the Self.--Nor is it true that the symbols are of the nature of the Self, because as being effects of Brahman they are of the nature of Brahman; for (from their being of the nature of Brahman) there results the non-existence of (them as) symbols. For the aggregate of names and so on can be viewed as of the nature of Brahman only in so far as the individual character of those effects of Brahman is sublated; and when that character is sublated how then can they be viewed as symbols, and how can the Self be apprehended in them? Nor does it follow from the fact of Brahman being the Self that a contemplation of the Self can be established on the ground of texts teaching a contemplation on Brahman (in certain symbols), since a contemplation of the latter kind does not do away with agentship and the like. For the instruction that Brahman is the Self depends on the doing away with agentship and all other characteristics of transmigratory existence; the injunction of meditations, on the other hand, depends on the non-removal of those characteristics. Hence we cannot establish the apprehension of the Self (in the symbols) on the ground of the meditating person being the same as the symbols. For golden ornaments and figures made of gold are not identical with each other, but only in so far as gold constitutes the Self of both. And that from that oneness (of symbol and meditating person) which depends on Brahman being the Self of all there results non-existence of the symbols (and hence impossibility of the meditations
enjoined), we have explained above.--For these reasons the Self is not contemplated in symbols.