The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
36. (The same thing follows) from the express denial of other (existences).
Having thus refuted the arguments of the pûrvapakshin, the Sûtrakâra in conclusion strengthens his view by a further reason. A great number of Vedic passages--which, considering the context in which they stand, cannot be explained otherwise--distinctly deny that there exists anything apart from Brahman; 'He indeed is below; I am below; the Self is below' (Kh. Up. VII, 25, 1; 2); 'Whosoever looks for anything elsewhere than in the Self was abandoned by everything' (Bri. Up. II, 4, 6); 'Brahman
alone is all this' (Mu. Up. II, 2, 11); 'The Self is all this' (Kh. Up. VII, 25, 2): 'In it there is no diversity' (Bri. Up. IV, 4, 19); 'He to whom there is nothing superior, from whom there is nothing different' (Svet. Up. III, 9); 'This is the Brahman without cause and without effect, without anything inside or outside' (Bri. Up. II, 5, 19).--And that there is no other Self within the highest Self, follows from that scriptural passage which teaches Brahman to be within everything (Bri. Up. II, 5, 19).