Charak Samhita
शीतोष्णस्निग्धरूक्षाद्यैरुपक्रान्ताश्च ये गदाः। सम्यक् साध्या न सिध्यन्ति रक्तजांस्तान् विभावयेत् ॥१७॥
The diseases, which, in spite of being curable, are not alleviated after treatment with any of six therapies like cold-hot, unctuous-rough etc. should be considered as caused by (impure) blood.
english translation
zItoSNasnigdharUkSAdyairupakrAntAzca ye gadAH। samyak sAdhyA na sidhyanti raktajAMstAn vibhAvayet ॥17॥
hk transliteration by Sanscript