The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
20. And as in the case of the different vital airs.
It is a matter of observation that when the operations of the different kinds of vital air--such as prâna the ascending vital air, apâna the descending vital air, &c.--are suspended, in consequence of the breath being held so that they exist in their causes merely, the only effect which continues to be accomplished is life, while all other effects, such as the bending and stretching of the limbs and so on, are stopped. When, thereupon, the vital airs again begin to act, those other effects also are brought about, in addition to mere life.--Nor must the vital airs, on account of their being divided into classes, be considered as something else than vital air; for wind (air) constitutes their common character. Thus (i. e. in the manner illustrated by the instance of the vital airs) the non-difference of the effect from the cause is to be conceived.--As, therefore, the whole world is an effect of Brahman and
non-different from it, the promise held out in the scriptural passage that 'What is not heard is heard, what is not perceived is perceived, what is not known is known' (Kh. Up. VI, 1, 3) is fulfilled 1.
343:1 Because it has been shown that cause and effect are identical; hence if the cause is known, the effect is known also.