The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut [1890] at sacred-texts.com
16. (The Self consisting of bliss is the highest Self,) not the other (i.e. the individual Soul), on account of the impossibility (of the latter assumption).
And for the following reason also the Self consisting of bliss is the highest Self only, not the other, i.e. the one which is other than the Lord, i.e. the transmigrating individual soul. The personal soul cannot be denoted by the term 'the one consisting of bliss.' Why? On account of the impossibility. For Scripture says, with reference to the Self consisting of bliss, 'He wished, may I be many, may I grow forth. He brooded over himself. After he had thus brooded, he sent forth whatever there is.' Here, the desire arising before the origination of a body, &c., the non-separation of the effects created from the creator, and the creation of all effects whatever, cannot possibly belong to any Self different from the highest Self.