Manava Dharmashastra 1.110

1.110

yāvatkiñcittapaḥ prāṇāyāmamaunayamaniyamakṛcchracāndrāyaṇānaśanādi tasya sarvasya phalaprasave mūlamācāro'tastameva munayastapaḥphalārthino mūlatvena kāraṇatayā jagṛhuḥ gṛhītavantaḥ | ācārādṛṣṭvā dharmasya munayo gatiṃ prāptimatikṛcchrakaraṃ tapastathāpyācārahīnasya na phalatīti śrutiḥ |

Having thus seen that virtue is got at from Right Behaviour, the sages regarded Right Behaviour as the very root of all Austerity.—(110)

Medhātithi’s commentary (manubhāṣya):
‘Of all Austerity,—i.e. Breath-control, silence, observances, self-control, and the busts of ‘Kṛcchra, Chāndrā yaṇa, and also absolute Fasting’;—of all this ‘Austerity,’ Right Behaviour is ‘the root,’—the direct cause, leading to the growth of their fruit.—For the reason given, the sages regarded, accepted, it as being the root,—i.e. the cause,—of Austerity, performed by men desiring results.—‘Having seen that virtue is got at,’—acquired—‘from Right Behaviour.’—However difficult the Austerity performed, it is not fruitful for the man that is without Right Behaviour so says the Śruti.—(111).