The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
34. In any case the same (duties have to be performed) on account of the twofold indicatory marks.
In any case, i.e. whether viewed as duties incumbent on the âsramas or as co-operating with knowledge, the very same agnihotra and other duties have to be performed.--What, it may be asked, does the teacher wish to preclude by the emphatic expression 'the very same?'--The suspicion, we reply, that those works might be separate works 1. In the ayana of the Kundapâyins indeed the injunctive statement,' They offer the agnihotra for a month 2,' enjoins a sacrifice different from the permanent (ordinary) agnihotra; but in our present case there is no analogous separation of works.--Why?--On account of the twofold indicatory mark; i.e. on account of both scripture and Smriti supplying indicatory marks. In the first place, the scriptural passage, 'Him the Brâhmanas seek to know through the study of the Veda,' &c., directs that sacrifices and the like--as things already established and the form of which is already in existence (viz. through previous injunctions)--are to be employed as means in the search for knowledge; and does not originate a new form of those works, while the passage quoted above, 'They offer the agnihotra for a month,' does originate a new separate sacrifice.--In the second place the Smriti-passage, 'He who performs the work to be done without aiming at the fruit of the work,' shows that the very same work which is already known as something to be performed subserves the origination of knowledge. Moreover the Smriti-passage, 'He who is qualified by those forty-eight purifications,' &c., refers to the purifications required for Vedic works, with a view to the origination of knowledge in him who has undergone those purifications.--The Sûtrakâra therefore rightly emphasizes the non-difference of the works.
314:1 That the works referred to in the Upanishads as means of knowledge, might be works altogether different from those enjoined in the karmakânda as means of bringing about certain special results such as the heavenly world.
314:2 See above, p. 250.