Ashtangasamgraha 1.2

1.2

athāta āyuṣkāmīyaṃ nāmādhyāyaṃ vyākhyāsyāmaḥ iti ha smā+āhurātreyādayo maharṣayaḥ ||

teṣāṃ puṇyabalena pṛthivyādīnāṃ sarvaguṇasamudāyādacintyarasa vīryādisamuditāni sasyānyoṣadhayaścāsan |

te tāni jitendriyatvāt kāle mātrayā copayuñjānāḥ satyārjavānṛśaṃsyādiguṇayogācca surasadṛśatejaso rūpākṛtipramāṇaprasādopacayasaṃhananasattvasārasampannā dīrghāyuṣo nīrujaśca babhūvuḥ ||

vidadhāti jvaraṃ doṣastasmāt kurvīta laṅghanam ||

Now, therefore, we shall explain the chapter named "The Desire for Long Life"; thus spoke the great sages, Ātreya and the others.

By the power of their merit, from the assemblage of all qualities of earth and the other elements, grains and medicinal herbs arose endowed with inconceivable tastes, potencies, and so forth.

Because they had conquered their senses, using these [herbs and grains] at the proper time and in proper measure, and through their practice of virtues such as truth, rectitude, and non-cruelty, they possessed radiance equal to the gods; were endowed with form, physique, proper proportion, clarity, fleshiness, compactness, mental vigor, and excellence of bodily tissues; and became long-lived and free from illness.

The doṣa brings about fever; therefore, one should perform fasting.