Manava Dharmashastra 4.13

4.13

vṛttiviṣayo vidhirvṛttiśabdenoktaḥ | tenānyatamayeti na tadapekṣamekajīvitam anyatamena vṛttividhānāt | ato vṛttisamuccayajīvinaḥ pitṛdhanaṃ prāptavataśca vratādhikāro na lupyate | anyathā ekavṛttijīvana eva syāt | vratānīmāni | mānasaḥ saṅkalpo ‘vrata’mucyate--‘śāstravihitamidaṃ mayā kartavyamidaṃ vā na kartavya’mityevam | svargyāyuṣyayaśasyāni vratadhāraṇaphalāni kecidāhuḥ | ataścaitatphalārthino vrateṣvadhikāraḥ | tadayuktam | anityatvameva sati prasajyeta | tatrottaraśloke nityagrahaṇaṃ bādhyaṃta | śrutau caiṣāṃ nityatā jñāpitā ‘yāvat hi enasā yukto bhavatīti’ | svargādīnāṃ kāmyatvenānvaye nādhikṛtaviśeṣaṇatvaṃ pratipadyeran |

The twice-born Accomplished Student, living by any one of these means of livelihood, should keep these (following) observances, which are conducive to heaven, longevity and fame.—(13)

Medhātithi’s commentary (manubhāṣya):
The term ‘means of livelihood’ stands for the rule regarding subsistence. Hence, ‘by any one’ does not imply that the man’s life should be entirely dependent upon that one; because the rules do not say that he who has recourse to one living should not have recourse to another. It is for this reason,too, that the mail subsisting by a number of means of living, or the man who has inherited his father’s property (and hence does not stand in need of the modes of living just described), does not cease to be entitled to the keeping of the observances. If this were not so, then it would be absolutely necessary for the man to adopt only one mode of living.

‘These observances.’—‘Observance’ means mental determination, in the form—‘such and such an act is enjoined by the scriptures,—I should do this—or I should not do that.’

‘Conducive to heaven, longevity and fame.’— Some people have held that this mentions the results actually following from the keeping of the observances; and hence it is only persons desiring these results, that have to keep the observances.

This, however, is not right. As if this were so, then the observances would cease to be obligatory; and this would be incompatible with the term ‘nitya,’ ‘daily,’ ‘always,’ occurring in the next verse. Further, the Veda has indicated the obligatory character of these observances:—‘By not keeping these, one becomes beset with sin,’ Further, if Heaven and the rest were construed as something desired, they could not attain the position of being qualifications of the persons entitled to the observances.—(13)

Comparative notes by various authors
Mahābhārata (12.249.25-28).—‘The man who carries on, without complaint, the functions of the householder, purifies ten ancestors and ten descendants.... For householders whose self is under control a place in heaven is effectively secured.’