The Compendium of Caraka 1.30.23

1.30.23

tadāyurvedayatītyāyurvedaḥ kathamiti cet ucyate svalakṣaṇataḥ sukhāsukhato hitāhitataḥ pramāṇāpramāṇātaśca yatścāyuṣyāṇyanāyuṣyāṇi ca dravyaguṇakarmāṇi vedayatyato 'apyāyurvedaḥ /

It makes known (vedayati) lifespan (āyus), hence it is Āyurveda. If it is asked 'How?': It is said: by its own characteristics, by happiness and unhappiness, by benefit and harm, and by its measure and non-measure; and because it makes known the substances, qualities, and actions that are conducive and non-conducive to lifespan, for this reason also it is Āyurveda.