The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
2. On account of the impossibility of a secondary (origin of the prânas).
Against the objection that the origin of the prânas must be understood in a secondary sense because the text states that they existed before the origin of the world, the Sûtrakâra declares 'on account of the impossibility of a secondary origin.' The statement as to the origin of the prânas cannot be taken in a secondary sense because therefrom would result the abandonment of a general assertion. For after the text has asserted that the knowledge of everything depends on the knowledge of one ('What is that through which when it is known everything else becomes known?' Mu. Up. I, 1, 3), it goes on to say, in order to prove that assertion, that 'From him is born prâna,' &c. (Mu. Up. II, 1, 3). Now the assertion is made good only if the whole world including the prânas is an effect of Brahman, because then there is no effect independent of the material cause; if on the other hand the statement as to the origin of the prânas were taken in a secondary sense, the assertion would thereby be stultified. The text, moreover, makes some concluding statements about the matter asserted, 'The Person is all this, sacrifice, penance, Brahman, the highest Immortal' (II, 1, 10), and 'Brahman alone is all this; it is the Best.'--That same
assertion is to be connected with such passages as the following, 'When we see, hear, perceive, and know the Self, then all this is known' (Bri. Up. II, 4, 5).--How then have we to account for the statement that the prânas existed before the creation?--That statement, we reply, does not refer to the fundamental causal substance; for we ascertain from scriptural passages, such as Mu. Up. II, 1, 2 ('That heavenly Person is without breath and without mind, pure, higher than the high Imperishable'), that the fundamental causal substance is devoid of all distinctions such as breath and the like. We must rather view the statement about the existence of the prânas before the creation as having for its object a subordinate causal substance 1, and being made with reference to the effects of the latter only. For it is known from Sruti and Smriti that even in the universe of evolved things many states of being may stand to each other in the relation of causal substance and effect.--In the adhikarana treating of the ether there occurred a Sûtra (composed of the same syllables) 'gaunyasambhavât,' which as being the pûrvapaksha-sûtra had to be explained as 'gaunî asambhavât,' 'the statement about the origin of ether must be taken in a secondary sense on account of the impossibility (of the primary sense).' There the final conclusion was established by means of the abandonment of the general assertion. Here on the other hand the Sûtra is the Siddhânta Sûtra and we have therefore explained it as meaning 'on account of the impossibility of a secondary meaning.'--Those who explain the present Sûtra in the same way as the previous Sûtra overlook the fact of the general assertion being abandoned (viz. if the passages referring to the origin of the prânas were taken in a secondary sense).
77:1 Such as Hiranyagarbha.