The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
39. And because it is declared by scripture.
We assume the Lord to bring about the fruits of actions, not only because no other assumption appears plausible, but also because we have direct scriptural statement on our side. Cp. e.g. the passage, 'This indeed is the great, unborn Self, the giver of food, the giver of wealth' (Bri. Up. IV. 4, 24).