The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
38. From him (i.e. the Lord, there comes) the fruit (of works); for (that only) is possible.
We now turn to another characteristic belonging to Brahman, in so far as it is connected with the every-day world in which we distinguish a ruler and the objects of his rule.--There arises the question whether the threefold fruits of action which are enjoyed by the creatures in their
samsâra-state--viz. pain, pleasure, and a mixture of the two-spring from the actions themselves or come from the Lord.--The Sûtrakâra embraces the latter alternative, on the ground that it is the only possible one. The ruler of all who by turns provides for the creation, the subsistence and the reabsorption of the world, and who knows all the differences of place and time, he alone is capable of effecting all those modes of requital which are in accordance with the merit of the agents; actions, on the other hand, which pass away as soon as done, have no power of bringing about results at some future time, since nothing can spring from nothing. Nor can the latter difficulty be overcome by the assumption that an action passes away only after having produced some result according to its nature, and that the agent will at some future time enjoy that fruit of his action. For the fruit of an action is such only through being enjoyed by the agent; only at the moment when some pleasure or some pain--the result of some deed--is enjoyed by the doer of the deed people understand it to be a 'fruit.'--Nor in the second place. have we the right to assume that the fruit will, at some future time, spring from the so-called supersensuous principle (apûrva), which itself is supposed to be a direct result of the deed; for that so-called supersensuous principle is something of non-intelligent nature, comparable to a piece of wood or metal, and as such cannot act unless moved by some intelligent being. And moreover there is no proof whatever for the existence of such an apûrva.--But is it not proved by the fact that deeds are actually requited?--By no means, we reply; for the fact of requital may be accounted for by the action of the Lord.