The Compendium of Caraka 6.3.110

6.3.110

sannipātajvaro 'asādhyaḥ kṛcchrasādhyastvato 'anyathā/
nidāne trividhā proktā yā pṛthagjajvarākṛtiḥ//

fever of toxic combination is incurable; otherwise, it is curable with difficulty. / The three forms of fever born of individual [doṣas] which were taught in the Nidāna [section],