The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
47. There is the injunction of something else cooperating (towards knowledge) (which is) a third thing (with regard to bâlya and pânditya), (which injunction is given) for the case (of perfect knowledge not yet having arisen) to him who is such (i.e. the Samnyâsin possessing knowledge); as in the case of injunctions and the like.
'Therefore let a Brâhmana after he has done with learning wish to stand by a childlike state; and after he has done with the childlike state and learning (he is, or, may be) a Muni; and after he has done with what constitutes Muniship and non-Muniship (he is, or, may be) a Brâhmana' (Bri. Up. III, 5). With reference to this passage a doubt arises whether it enjoins the state of a Muni or not.--The pûrvapakshin maintains that it does not enjoin it, since the injunction is completed with the clause, 'Let him wish to stand by a childlike state.' The following clause 'then a Muni' contains no verbal form of injunctive force and therefore must be viewed as a mere anuvâda (making a remark concerning the state of a Muni which is already established). Should it be asked how this conclusion is reached, we reply that Muniship is established by the clause 'having done with learning' (which forms part of the injunctive portion of the passage), as 'Muni' and 'learned man' both denote knowledge 1. It is, moreover, clear also that the last clause,' and after he has done with what constitutes Muniship and non-Muniship (he is) a Brâhmana,' does not enjoin the condition of a Brâhmana, as that state is previously established (independently of that clause); but the words 'then a Brâhmana' are a mere glorificatory anuvâda. Now as the words 'then a Muni' show an analogous form of enunciation (to the clause 'then a Brâhmana'), they also can embody a glorificatory anuvâda only.
To all this we reply as follows. 'There is an injunction of something else which co-operates.' The passage must be understood as enjoining the state of a Muni--which co-operates towards knowledge--in the same way as it enjoins learning and a childlike state, because that state is something new (not enjoined before).--But it has been said above that the word 'learning' already intimates Muniship!--This, we reply, does not invalidate our case since the word 'muni' denotes (not only knowledge as the term 'learned man' does, but) pre-eminence of knowledge, on the ground as well of its etymology from 'manana,' i.e. thinking, as of common use, shown in such phrases as 'I am the Vyâsa of Munis also.'--But the term 'Muni' is also seen to denote the last order of life; cp. passages such as 'Householdership, studentship, the order of Munis, the order of hermits in the woods.'--Yes, but it has not that meaning exclusively, as we see that it does not apply to phrases such as 'Valmîki is the foremost among Munis.' In the passage quoted (about the four orders) the last order is referred to, by the term 'Muni,' because there it stands in proximity to the other orders of life, and, as the state of the Ascetic is the only one which remains (after we have assigned the three other terms to the stages of life clearly denoted by them), the last order may be denoted 'mauna' because knowledge is its principal requirement.--We therefore conclude that in the passage under discussion the state of the Muni--whose characteristic mark is pre-eminence of knowledge--is enjoined as something third--with regard to the childlike state and learning.--Against the objection that the injunction terminates with the childlike state, we remark that all the same we must view the Muniship also as something enjoined, as it is something new, so that we have to supplement the clause as follows: 'then he is to be a Muni.' That the state of a Muni is something to be enjoined, in the same way as the childlike state and 'earning, also follows from its being referred to as something to be done with (like bâlya and pânditya. It is enjoined 'on him who is such,' i.e. on the Samnyâsin possessing knowledge.--How do we know this latter point?--Because
the Samnyâsin who possesses knowledge forms the topic, as we see from the preceding passage, 'Having cognized the Self and risen above the desire for sons, &c., they wander about as mendicants.'--But if the Samnyâsin possesses knowledge, pre-eminence of knowledge is already established thereby; what then is the use of the injunction of Muniship?--To this the Sûtra replies 'in the case of.' That means: in the case of pre-eminence of knowledge not being established owing to the prevailing force of the (erroneous) idea of multiplicity; for that case the injunction (of Muniship, i.e. of pre-eminence of knowledge) is given. 'As in the case of injunctions and the like.' With reference to sacrifices such as are enjoined in the passage, 'He who is desirous of the heavenly world is to offer the darsapûrnamâsa-sacrifice,' the aggregate of subordinate members, such as the establishment of the sacred fires, is enjoined as something helpful; similarly in this text whose topic is knowledge and which therefore does not chiefly aim at injunction, Muniship is enjoined as something helpful to knowledge.
As thus the order of the ascetic, as distinguished by a childlike state and so on, is actually established by scripture, for what reason does the Khândogya Upanishad wind up with the householder, viz. in the passage, 'After having received his discharge from his teacher he settles in his own house,' &c.? For by concluding with the householder, scripture manifests special regard for him.--To this doubt the next Sûtra replies.
322:1 The state of a Muni is already enjoined by the clause 'pândityam nirvidya;' the clause 'atha munih,' therefore, may be viewed as an anuvâda (as which it could not be viewed, if there were no previous injunction of mauna).