The Compendium of Caraka 3.3.40_1

3.3.40_1

jvaro hyāmāśayasamutthaḥ, prāyo bheṣajāni cāmāśayasamutthānāṃ vikārāṇāṃ *pācanavamanāpatarpaṇasamarthāni bhavanti; pācanārthaṃ ca pānīyamuṣṇaṃ, tasmādetajjvaritebhyaḥ prayacchanti bhiṣajo bhūyiṣṭham/

For fever arises from the stomach, and medicines for disorders arising from the stomach are generally capable of digestive maturation, emesis, and reducing therapy; and hot water is for digestive maturation. Therefore, physicians generally give it to those with fever.