The Compendium of Caraka 1.10.3

1.10.3

catuṣpādaṃ ṣoḍaśakalaṃ bheṣajamiti bheṣajo bhāṣante, yaduktaṃ pūrvādhyāye ṣoḍaśaguṇamiti, tadbheṣajaṃ yuktiyuktamalamārogyāyeti bhagavān punarvasurātreyaḥ //

'Medicine consists of four pillars and sixteen constituents,' so physicians declare, referring to what was described in the preceding chapter as having sixteen qualities; 'that medicine, properly administered, is sufficient for health,' said the venerable Punarvasu Ātreya.