Charak Samhita
तस्मादायुःप्रकर्षार्थं प्राणकामैःसुखार्थिभिः। रसायनविधिः सेव्यो विधिवत्सुसमाहितैः ॥२२॥
Hence those who desire longevity, vital strength and happiness should use the Rasayana methodically and carefully.
english translation
tasmAdAyuHprakarSArthaM prANakAmaiHsukhArthibhiH। rasAyanavidhiH sevyo vidhivatsusamAhitaiH ॥22॥
hk transliteration by Sanscript