The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
23. (Brahman is) the material cause also, on account of (this view) not being in conflict with the promissory statements and the illustrative instances.
It has been said that, as practical religious duty has to be enquired into because it is the cause of an increase of happiness, so Brahman has to be enquired into because it is the cause of absolute beatitude. And Brahman has been defined as that from which there proceed the origination, sustentation, and retractation of this world. Now as this definition comprises alike the relation of substantial causality in which clay and gold, for instance, stand to golden ornaments and earthen pots, and the relation of operative
causality in which the potter and the goldsmith stand to the things mentioned; a doubt arises to which of these two kinds the causality of Brahman belongs.
The pûrvapakshin maintains that Brahman, evidently is the operative cause of the world only, because Scripture declares his creative energy to be preceded by reflection. Compare, for instance, Pra. Up. VI, 3; 4: 'He reflected, he created prâna.' For observation shows that the action of operative causes only, such as potters and the like, is preceded by reflection, and moreover that the result of some activity is brought about by the concurrence of several factors 1. It is therefore appropriate that we should view the prime creator in the same light. The circumstance of his being known as 'the Lord' furnishes another argument. For lords such as kings and the son of Vivasvat are known only as operative causes, and the highest Lord also must on that account be viewed as an operative cause only.--Further, the effect of the creator's activity, viz. this world, is seen to consist of parts, to be non-intelligent and impure; we therefore must assume that its cause also is of the same nature; for it is a matter of general observation that cause and effect are alike in kind. But that Brahman does not resemble the world in nature, we know from many scriptural passages, such as 'It is without parts, without actions, tranquil, without fault, without taint' Sve. Up. VI, 19). Hence there remains no other alternative but to admit that in addition to Brahman there exists a material cause of the world of impure nature, such as is known from Smriti 2, and to limit the causality of Brahman, as declared by Scripture, to operative causality.
To this we make the following reply.--Brahman is to be acknowledged as the material cause as well as the operative cause; because this latter view does not conflict with the promissory statements and the illustrative instances. The promissory statement chiefly meant is the following one,
[paragraph continues] 'Have you ever asked for that instruction by which that which is not heard becomes heard; that which is not perceived, perceived; that which is not known, known?'(Kh. Up. VI, 1, 3.) This passage intimates that through the cognition of one thing everything else, even if (previously) unknown, becomes known. Now the knowledge of everything is possible through the cognition of the material cause, since the effect is non-different from the material cause. On the other hand, effects are not non-different from their operative causes; for we know from ordinary experience that the carpenter, for instance, is different from the house he has built.--The illustrative example referred to is the one mentioned (Kh. Up. VI, 1, 4), 'My dear, as by one clod of clay all that is made of clay is known, the modification (i.e. the effect) being a name merely which has its origin in speech, while the truth is that it is clay merely;' which passage again has reference to the material cause. The text adds a few more illustrative instances of similar nature, 'As by one nugget of gold all that is made of gold is known; as by one pair of nail-scissors all that is made of iron is known.'--Similar promissory statements are made in other places also, for instance, 'What is that through which if it is known everything else becomes known?' (Mu. Up. I, 1, 3.) An illustrative instance also is given in the same place, 'As plants grow on the earth' (I, 1, 7).--Compare also the promissory statement in Bri. Up. IV, 5, 6, 'When the Self has been seen, heard, perceived, and known, then all this is known;' and the illustrative instance quoted (IV, 5, 8), 'Now as the sounds of a drum if beaten cannot be seized externally, but the sound is seized when the drum is seized or the beater of the drum.'--Similar promissory statements and illustrative instances which are to be found in all Vedânta-texts are to be viewed as proving, more or less, that Brahman is also the material cause of the world. The ablative case also in the passage, 'That from whence (yatah) these beings are born,' has to be considered as indicating the material cause of the beings, according to the grammatical rule, Pân. I, 4, 30.--That Brahman is at the same time the operative cause of the
world, we have to conclude from the circumstance that there is no other guiding being. Ordinarily material causes, indeed, such as lumps of clay and pieces of gold, are dependent, in order to shape themselves into vessels and ornaments, on extraneous operative causes such as potters and goldsmiths; but outside Brahman as material cause there is no other operative cause to which the material cause could look; for Scripture says that previously to creation Brahman was one without a second.--The absence of a guiding principle other than the material cause can moreover be established by means of the argument made use of in the Sûtra, viz. accordance with the promissory statements and the illustrative examples. If there were admitted a guiding principle different from the material cause, it would follow that everything cannot be known through one thing, and thereby the promissory statements as well as the illustrative instances would be stultified.--The Self is thus the operative cause, because there is no other ruling principle, and the material cause because there is no other substance from which the world could originate.
284:1 I.e. that the operative cause and the substantial cause are separate things.
284:2 Viz. the Sânkhya-smriti.