The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
33. But the (denials of) conceptions concerning the
akshara are to be comprehended (in all meditations on the akshara), on account of the equality and of the object being the same, as in the case of the upasad; this has been explained (in the Pûrva Mîmâmsâ).
We read in the Vâgasaneyaka, 'O Gârgî, the Brâhmanas call this the Akshara. It is neither coarse, nor fine, nor short, nor long,' &c. (Bri. Up. III, 8, 8). Similarly the Âtharvana says, 'The higher knowledge is that by which the Indestructible is apprehended. That which cannot be seen nor seized, which has no family and no caste,' &c. (Mu. Up. I, 1, 5; 6). In other places also the highest Brahman, under the name of Akshara, is described as that of which all qualities are to be denied. Now in some places qualities are denied of Brahman which are not denied in other places, and hence a doubt arises whether the mental conception of these particular denials is to form part of all those passages or not.
To the assertion of the pûrvapakshin that each denial is valid only for that passage in which the text actually exhibits it, we make the following reply.--The conceptions of the akshara, i.e. the conceptions of the particular denials concerning the akshara, are to be included in all those passages, 'on account of the equality and on account of the same object being referred to.' The equality consists therein that all the texts alluded to convey an idea of Brahman in the same way, viz. by denying of it all attributes; and we recognise in all of them the same object of instruction, viz. the one undivided Brahman. Why then should the conceptions stated in one passage not be valid for all others also? To the present case the same argumentation applies which had been made use of under III, 3, 11. There positive attributes were discussed; here we are concerned with negative ones. The division of the discussion into two (instead of disposing of positive and negative attributes in one adhikarana) is due to the wish of explaining the differences in detail. The clause, 'as in the case of the upasads,' introduces a parallel case. For
the Gâmadagnya-ahîna-sacrifice 1 the text enjoins that the upasad offerings are to consist of purodâsas. Now although the mantras accompanying the offering of the purodâsas are originally enjoined in the Veda of the Udgâtris (Tândya Brâ. XXI, 10, 11, 'Agni, promote the hotra,' &c.), yet they are to be enounced by the adhvaryu; for the offering of the purodâsas is the work of the adhvaryu, and subordinate matters (i.e. here, the mantras) are governed by the principal matter (i.e. the offering of the purodâsa). Similarly, in the case under discussion, the attributes of the akshara have, because they are subordinate to the akshara itself, to be connected with the latter everywhere, in whatever places the text may originally state them.--The principle of decision employed is explained in the Pûrva Mîmâmsâ-sûtras III, 3, 9.
238:1 Api ka nâdhikâravatâm sarveshâm rishînâm âtmatattvagñânam tenâvyâpakoऽpy ayam pûrvapaksha ity âha gñânântarushu keti. Bhâ.