The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
6. Or that (viz. the concealment of the soul's powers springs) from its connexion with the body.
But if the soul is a part of the highest Self, why should its knowledge and lordship be hidden? We should rather
expect them to be as manifest as the light and the heat of the spark.--True, we reply; but the state of concealment of the soul's knowledge and lordship is due to its being joined to a body, i.e. to a body, sense-organs, mind, buddhi, sense-objects, sensations, &c. And to this state of things there applies the simile: As the heat and light of the fire are hidden as long as the fire is still hidden in the wood from which it will be produced by friction, or as long as it is covered by ashes; so, in consequence of the soul being connected with limiting adjuncts in the form of a body, &c., founded on name and form as presented by Nescience, its knowledge and lordship remain hidden as long as it is possessed by the erroneous notion of not being distinct from those adjuncts.--The word 'or' in the Sûtra is meant to discard the suspicion that the Lord and the soul might be separate entities.--But why should not the soul be separate from the Lord, considering the state of concealment of its knowledge and power? If we allow the two to be fundamentally separate, we need not assume that their separateness is due to the soul's connexion with the body.--It is impossible, we reply, to assume the soul to be separate from the Lord. For in the scriptural passage beginning with 'That divinity thought' &c. (Kh. Up. VI, 3, 2) we meet with the clause, 'It entered into those beings with this living Self (gîva âtman); where the individual soul is referred to as the Self. And then we have the other passage, 'It is the True; it is the Self; that art thou, O Svetaketu,' which again teaches that the Lord is the Self of the soul. Hence the soul is non-different from the Lord, but its knowledge and power are obscured by its connexion with the body. From this it follows that the dreaming soul is not able to create, from its mere wishes, chariots and other things. If the soul possessed that power, nobody would ever have an unpleasant dream; for nobody ever wishes for something unpleasant to himself.--We finally deny that the scriptural passage about the waking state ('dream is the same as the place of waking' &c.) indicates the reality of dreams. The statement made there about the equality of the two states
is not meant to indicate that dreams are real, for that would conflict with the soul's self-luminousness (referred to above), and scripture, moreover, expressly declares that the chariots, &c., of a dream have no real existence; it merely means that dreams, because due to mental impressions (vâsanâ) received in the waking state, are equal to the latter in appearance.--From all this it follows that dreams are mere illusion.