The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
44. To the lord (of the sacrifice) only (the agent-ship in meditations belongs), because scripture declares a fruit; this is the view of Âtreya.
With regard to meditations on subordinate members of sacrificial actions there arises a doubt whether they are to be carried out by the sacrificer (i.e. him for whom the sacrifice is performed) or by the officiating priests.--By the sacrificer, the pûrvapakshin maintains, because scripture declares fruits. For a fruit is declared in such texts as the following one, 'There is rain for him, and he brings rain for others who thus knowing meditates on the fivefold Sâman as rain' (Kh. Up. II, 3, 2); and we must conclude that that fruit goes to the Lord of the sacrifice, because it is he who is entitled to the sacrificial performance together with its subordinate members, and because such meditations fall within the sphere of that to which he is entitled. And that the fruit belongs to him who carries out the meditations scripture states when saying, 'There is rain for him who meditates.'--But scripture declares a fruit for the priest also, viz. in the passage, 'Whatever desire he may desire either for himself or for the sacrificer he obtains by his singing.'--That passage, we reply, is of no force because it expressly declares the fruit (as belonging to the priest in a special case only). Hence the lord of the sacrifice only
is the agent in those meditations which have a fruit, this is the opinion of the teacher Âtreya.