Charak Samhita
युगपच्चानुपद्यन्ते नियमात् सन्तते ज्वरे। स शुद्ध्या वाऽप्यशुद्ध्या वा रसादीनामशेषतः ॥५७॥
If the involved factors like rasa are purified optimally the fever gets subsided in either 7 or 10 or 12 days, otherwise, the fever kills the patient within that period.
english translation
yugapaccAnupadyante niyamAt santate jvare। sa zuddhyA vA'pyazuddhyA vA rasAdInAmazeSataH ॥57॥
hk transliteration by Sanscript