The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut [1896] at sacred-texts.com

37. Thereby the omnipresence (of Brahman is established), in accordance with the statements about (Brahman's) extent.

The preceding demonstration that the texts calling Brahman a bank, and so on, are not to be taken literally, and that, on the other hand, the texts denying all plurality must be accepted as they stand., moreover, serves to prove that the Self is omnipresent. If the former texts were taken literally, banks and the like would have to be looked upon as belonging to the Self, and thence it would follow that the Self is limited. And if the texts of the latter class were not accepted as valid, there would be substances exclusive of each other, and thus the Self would again be limited.--That the Self is omnipresent follows from the texts proclaiming its extent, &c., cp. Kh. Up. VIII, 1, 3, 'As large as this ether is, so large is that ether within the heart;' 'Like the ether, he is omnipresent and eternal;' 'He is greater than the sky, greater than the ether' (Sat. Br. X, 6, 3, 2); 'He is eternal, omnipresent, firm, immoveable' (Bha. Gîtâ II, 24); and other similar passages from Sruti and Smriti.