The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
7. And common (to him who knows and him who does not know) (is the departure) up to the beginning of the way; and the immortality (of him who knows) (is relative only) without having burned (nescience and so on).
The question here arises whether the departure of the soul, as described hitherto, is the same in the case of him who knows and him who is destitute of knowledge; or whether there is any difference.--There is a difference, the pûrvapakshin maintains. For the departure as described has for its abode the elements, and this abiding in the elements is for the purpose of a new birth. But he who possesses true knowledge cannot be born again, since scripture declares that 'He who knows reaches immortality.' Hence only he who is devoid of knowledge departs in the way described.--But as that departure is described in chapters treating of knowledge it can belong only to him
who knows!--Not so, the pûrvapakshin replies. In the same way as sleep and the like, the departure of the soul is only referred to in the texts as something established elsewhere (not as something to be taught as part of true knowledge). Passages such as 'When a man sleeps,--is hungry,--is thirsty' (Kh. Up. VI, 8), although forming part of chapters concerned with true knowledge, mention sleep and so on which are common to all living beings, because they assist the comprehension of the matter to be taught, but do not aim at enjoining them specially for those who know. Analogously the texts about the soul's departure refer to that departure only in order to teach that 'that highest deity in which the heat of the dying man is merged, that is the Self, that art thou.' Now that departure is (in other scriptural passages) specially denied of him who knows; it therefore belongs to him only who does not know.
To this we make the following reply. That departure which is described in the passage, 'speech is merged in mind,' &c., must be 'common' to him who knows and him who does not know 'up to the beginning of the way;' because scripture records no distinction. The soul destitute of true knowledge having taken its abode in the subtle elements which constitute the seed of the body and being impelled by its works, migrates into a new body; while the soul of him who knows passes into the vein, revealed by true knowledge, which is the door of release. In this sense the Sûtra says 'up to the beginning of the way.'--But he who knows reaches immortality, and immortality does not depend on a change of place; why then should the soul take its abode in the elements or set out on a journey?--That immortality, we reply, is 'without having burned.' i.e. for him who, without having altogether burned nescience and the other afflictions, is about to obtain, through the power of the lower knowledge, a relative immortality only, there take place the entering on the way and the abiding in the elements. For without a substratum the prânas could not move. There is thus no difficulty.