The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
13. But on account of the indicatory mark supplied by their reflecting (i.e. by the reflection attributed to the elements), he (i.e. the Lord is the creative principle abiding within the elements).
A doubt here arises whether ether and the other elements do themselves send forth their effects, or if the highest Lord abiding within certain Selfs produces, after reflection, certain effects.
Here the pûrvapakshin maintains that the elements themselves send forth, because the texts speak of them as acting independently; compare, for instance, 'from ether sprang air, from air fire,' &c. The objection that non-intelligent beings cannot enter on independent activity is invalidated by the fact that the elements also are spoken of in the sacred texts as endowed with intelligence, cf. for instance, 'fire thought,' 'water thought' (Kh. Up. VI, 2, 3; 4).
To this we reply that the highest Lord himself abiding within certain Selfs sends forth, after reflection, certain effects.--Why?--On account of the indicatory marks. For
texts such as 'he who dwells in the earth, and within the earth, whom the earth does not know, whose body the earth is and who rules the earth within' show that the elements enter on their activity only if presided over by an intelligent principle. Texts such as 'He became sat and tyat' (which occurs in the passage, 'he wished may I be many, may I grow forth,' Taitt. Up. 11, 6) and 'It made itself its Self' (i.e. the Self of everything which exists; II, 7) show that he the highest Lord) is the Self of everything. The thinking and hearing which the texts attribute to water and fire must be viewed as due to the fact of the highest Lord having entered them; for the passage, 'there is no other seer but he,' denies there being any other seer (thinker), and that which is (i.e. Brahman), in the character of seer (or thinker), constitutes the subject-matter of the whole chapter; as we conclude from the introductory passage, 'It thought, may I be many, may I grow forth' (Kh. Up. VI, 2, 3).