The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut [1890] at sacred-texts.com

24. If you object on the ground of the observation of the employment (of instruments); (we say), No; because as milk (transforms itself, so Brahman does).

Your assertion that the intelligent Brahman alone, without a second, is the cause of the world cannot be maintained, on account of the observation of employment (of instruments). For in ordinary life we see that potters, weavers, and other handicraftsmen produce jars, cloth, and the like, after having put themselves in possession of the means thereto by providing themselves with various implements, such as clay, staffs, wheels, string, &c.; Brahman, on the other hand, you conceive to be without any help; how then can it act as a creator without providing itself with instruments to work with? We therefore maintain that Brahman is not the cause of the world.

in consequence of a peculiar constitution of the causal substance, as in the case of milk. Just as milk and water turn into curds and ice respectively, without any extraneous means, so it is in the case of Brahman also. And if you object to this analogy for the reason that milk, in order to turn into curds, does require an extraneous agent, viz. heat, we reply that milk by itself also undergoes a certain amount of definite change, and that its turning is merely accelerated by heat. If milk did not possess that capability of itself, heat could not compel it to turn; for we see that air or ether, for instance, is not compelled by the action of heat to turn into sour milk. By the co-operation of auxiliary means the milk's capability of turning into sour milk is merely completed. The absolutely complete power of Brahman, on the other hand, does not require to be supplemented by any extraneous help. Thus Scripture also declares, 'There is no effect and no instrument known of him, no one is seen like unto him or better; his high power is revealed as manifold, as inherent, acting as force and knowledge' (Sve. Up. VI, 8). Therefore Brahman, although one only, is, owing to its manifold powers, able to transform itself into manifold effects; just as milk is.