The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
35. And because (only such a connexion) is possible.
Moreover, only such a connexion as described above is possible. For scriptural passages, such as 'He is gone to his Self (Kh. Up. VI, 8, 1), declare that the connexion of the soul with the highest Self is one of essential nature. But as the essential nature of a thing is imperishable, the connexion cannot be analogous to that of the inhabitants with the town, but can only be explained with reference to an obscuration, owing to Nescience, of the soul's true nature.--Similarly the difference spoken of by scripture cannot be real, but only such as is due to Nescience; for many texts declare that there exists only one Lord. Analogously, scripture teaches that the one ether is made manifold as it were by its connexion with different places 'The ether which is outside man is the ether which is inside man, and the ether within the heart' (Kh. Up. III, 12, 7 ff.).