The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
8. (It cannot be maintained that agâ means the
pradhâna) because no special characteristic is stated; as in the case of the cup.
Here the advocate of the pradhâna comes again forward and maintains that the absence of scriptural authority for the pradhâna is not yet proved. For, he says, we have the following mantra (Sve. Up. IV, 5), 'There is one agâ 1, red, white, and black, producing manifold offspring of the same nature. There is one agâ who loves her and lies by her; there is another who leaves her after having enjoyed her.'--In this mantra the words 'red,' 'white,' and 'black' denote the three constituent elements of the pradhâna. Passion is called red on account of its colouring, i.e. influencing property; Goodness is called white, because it is of the nature of Light; Darkness is called black on account of its covering and obscuring property. The state of equipoise of the three constituent elements, i.e. the pradhâna, is denoted by the attributes of its parts, and is therefore called red-white-black. It is further called agâ, i.e. unborn, because it is acknowledged to be the fundamental matter out of which everything springs, not a mere effect.--But has not the word agâ the settled meaning of she-goat?--True; but the ordinary meaning of the word cannot be accepted in this place, because true knowledge forms the general subject-matter.--That pradhâna produces many creatures participating in its three constituent elements. One unborn being loves her and lies by her, i.e. some souls, deluded by ignorance, approach her, and falsely imagining that they experience pleasure or pain, or are in a state of dulness, pass through the course of transmigratory existence. Other souls, again, which have attained to discriminative knowledge, lose their attachment to prakriti, and leave her after having enjoyed her, i.e. after she has afforded to them enjoyment and release.--On the ground of this passage, as interpreted above, the
followers of Kapila claim the authority of Scripture for their pradhâna hypothesis.
To this argumentation we reply, that the quoted mantra by no means proves the Sânkhya doctrine to be based on Scripture. That mantra, taken by itself, is not able to give additional strength to any doctrine. For, by means of some supposition or other, the terms agâ, &c. can be reconciled with any doctrine, and there is no reason for the special assertion that the Sânkhya doctrine only is meant. The case is analogous to that of the cup mentioned in the mantra, 'There is a cup having its mouth below and its bottom above' (Bri. Up. II, 2, 3). Just as it is impossible to decide on the ground of this mantra taken by itself what special cup is meant--it being possible to ascribe, somehow or other, the quality of the mouth being turned downward to any cup--; so here also there is no special quality stated, so that it is not possible to decide from the mantra itself whether the pradhâna is meant by the term agâ, or something else.--But in connexion with the mantra about the cup we have a supplementary passage from which we learn what kind of cup is meant, 'What is called the cup having its mouth below and its bottom above is this head.'--Whence, however, can we learn what special being is meant by the agâ of the Svetâsvatara-upanishad?--To this question the next Sûtra replies.
253:1 As the meaning of the word agâ is going to be discussed, and as the author of the Sûtras and Sankara seem to disagree as to its meaning (see later on), I prefer to leave the word untranslated in this place.--Sankara reads--and explains,--in the mantra, sarûpâh (not sarûpâm) and bhuktabhogâm, not bhuktabhogyâm.