The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut [1896] at sacred-texts.com
4. And on account of the word (of the Veda).
The word of the Veda also proclaims the non-originatedness of ether; for it declares that 'air and ether (antariksha) are immortal' (Bri. Up. II, 3, 3), and what is immortal cannot have an origin. Another scriptural passage ('omnipresent and eternal like ether'), by comparing two attributes of Brahman, viz. omnipresence and eternity with the other, intimates that those qualities belong to the ether
also; in which case no beginning can be attributed to it. Other passages to be quoted in this connexion are, 'As this ether is infinite, so the Self is to be known as infinite;' and 'Brahman has the ether for its body, the ether is the Self.' For if the ether had a beginning, it could not be predicated of Brahman (as is done in the last passage), as we predicate blueness of a lotus ('the lotus is blue'). Hence we understand that the eternal Brahman is of the nature as ether.