The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
3. Thereby the Yoga (Smriti) is refuted.
This Sûtra extends the application of the preceding argumentation, and remarks that by the refutation of the Sânkhya-smriti the Yoga-smriti also is to be considered as refuted; for the latter also assumes, in opposition to Scripture, a pradhâna as the independent cause of the world, and the 'great principle,' &c. as its effects, although neither the Veda nor common experience favour these views.--But, if the same reasoning applies to the Yoga also, the latter system is already disposed of by the previous arguments; of what use then is it formally to extend them to the Yoga? (as the Sûtra does.)--We reply that here an additional
cause of doubt presents itself, the practice of Yoga being enjoined in the Veda as a means of obtaining perfect knowledge; so, for instance, Bri. Up. II, 4, 5, '(The Self) is to be heard, to be thought, to be meditated upon 1.' In the Svetâsvatara Upanishad, moreover, we find various injunctions of Yoga-practice connected with the assumption of different positions of the body; &c.; so, for instance, 'Holding his body with its three erect parts even,' &c. (II, 8).
Further, we find very many passages in the Veda which (without expressly enjoining it) point to the Yoga, as, for instance, Ka. Up. II, 6, 11, 'This, the firm holding back of the senses, is what is called Yoga;' 'Having received this knowledge and the whole rule of Yoga' (Ka. Up. II, 6, 18); and so on. And in the Yoga-sâstra itself the passage, 'Now then Yoga, the means of the knowledge of truth,' &c. defines the Yoga as a means of reaching perfect knowledge. As thus one topic of the sâstra at least (viz. the practice of Yoga) is shown to be authoritative, the entire Yoga-smriti will have to be accepted as unobjectionable, just as the Smriti referring to the ashtakâs 2.--To this we reply that the formal extension (to the Yoga, of the arguments primarily directed against the Sânkhya) has the purpose of removing the additional doubt stated in the above lines; for in spite of a part of the Yoga-smriti being authoritative, the disagreement (between Smriti and Sruti) on other topics remains as shown above.--Although 3 there are many Smritis treating of the soul, we have singled out for refutation the Sânkhya and Yoga because they are widely known as offering the means for accomplishing the highest
end of man and have found favour with many competent persons. Moreover, their position is strengthened by a Vedic passage referring to them, 'He who has known that cause which is to be apprehended by Sânkhya and Yoga he is freed from all fetters' (Sve. Up. VI, 13). (The claims which on the ground of this last passage might be set up for the Sânkhya and Yoga-smritis in their entirety) we refute by the remark that the highest beatitude (the highest aim of man) is not to be attained by the knowledge of the Sânkhya-smriti irrespective of the Veda, nor by the road of Yoga-practice. For Scripture itself declares that there is no other means of obtaining the highest beatitude but the knowledge of the unity of the Self which is conveyed by the Veda, 'Over death passes only the man who knows him; there is no other path to go' (Sve. Up. Ill, 8). And the Sânkhya and Yoga-systems maintain duality, do not discern the unity of the Self. In the passage quoted ('That cause which is to be apprehended by Sânkhya and Yoga') the terms 'Sânkhya' and 'Yoga' denote Vedic knowledge and meditation, as we infer from proximity 1. We willingly allow room for those portions of the two systems which do not contradict the Veda. In their description of the soul, for instance, as free from all qualities the Sânkhyas are in harmony with the Veda which teaches that the person (purusha) is essentially pure; cp. Bri. Up. IV, 3, 16. 'For that person is not attached to anything.' The Yoga again in giving rules for the condition of the wandering religious mendicant admits that state of retirement from the concerns of life which is known from scriptural passages such as the following one, 'Then the parivrâgaka with discoloured (yellow) dress, shaven, without any possessions,' &c. (Gâbâla Upan. IV).
The above remarks will serve as a reply to the claims of all argumentative Smritis. If it be said that those Smritis also assist, by argumentation and proof, the cognition of truth, we do not object to so much, but we maintain
all the same that the truth can be known from the Vedânta-texts only; as is stated by scriptural passages such as 'None who does not know the Veda perceives that great one' (Taitt. Br. III, 12, 9, 7); 'I now ask thee that person taught in the Upanishads' (Bri. Up, III, 9, 26); and others.
297:1 In which passage the phrase 'to be meditated upon' (nididhyâsâ) indicates the act of mental concentration characteristic of the Yoga.
297:2 The ashtakâs (certain oblations to be made on the eighth days after the full moons of the seasons hemanta and sisira) furnish the stock illustration for the doctrine of the Pûrvâ Mim. that Smriti is authoritative in so far as it is based on Sruti.
297:3 But why--it will be asked--do you apply yourself to the refutation of the Sânkhya and Yoga only, and not also to that of other Smritis conflicting with the Vedânta views?
298:1 I. e. from the fact of these terms being employed in a passage standing close to other passages which refer to Vedic knowledge.