Śaṅkaraon Brahma Sūtra 2.3.31

As in ordinary life virile power and so on, existing potentially only in young children, and being then looked upon as non-existing, become manifest at the time of puberty—and do not originate at that time from previous non-existence, because in that case they might originate in eunuchs also—; so the connexion of the soul y^ith the buddhi exists potentially merely during deep sleep and the period of general retractation, and again becomes manifest at the time of waking and the time of creation.—- This explanation is appropriate, because nothing can be assumed to spring up unless from something else ; other- wise we should have to suppose that effects spring up without causes. That the rising from deep sleep is due to the existence of potential avidyA, scripture also declares, ‘ Having become merged in the True they know not that they are merged in the True. Whatever these creatures — are here, whether a lion or a wolf,’ &c. {Kh. Up. VI, 9, % 3). It is therefore a proved matter that the connexion of the soul with the buddhi and the other adjuncts lasts as long as the soul (in its sa;«s^Lra-state).