The Compendium of Caraka 1.30.25

1.30.25

pramāṇamāyuṣastvarthendriyamanobuddhiceṣṭādīnāṃ vikṛtilakṣaṇairupalabhyate 'animittaiḥ ayamasmāt kṣaṇānmuhūrtāddivasāttripañcasaptadaśadvādaśāhāt pakṣānmāsāt ṣaṇmāsāt saṃvatsarādvā svabhāvāmāpatsyata iti tatra svabhāvaḥ pravṛtteruparamo maraṇamanityatā nirodha ityeko 'arthaḥ ityāyuṣaḥ pramāṇam ato viparītamapramāṇamariṣṭādhikāre dehaprakṛtilakṣaṇamadhikṛtya copadiṣṭamāyuṣaḥ pramāṇamāyurvede //

The measure of lifespan, however, is apprehended through uncaused signs of alteration in sense objects, sense organs, mind, intellect, actions, and the like, [indicating that] this person, after this moment, muhūrta, day, three, five, seven, ten, or twelve days, a fortnight, a month, six months, or a year, will attain to his intrinsic nature. There, intrinsic nature, cessation of activity, death, impermanence, and cessation are one and the same meaning. Such is the measure of lifespan; the opposite of this is non-measure. In the section on fatal prognostics, and by referring to the signs of constitution of the body, the measure of lifespan is taught in Āyurveda.