Shiva Purana
यथैकं च सुवर्णादि मिलितं रजतादिना ॥ अल्पमूल्यं प्रजायेत तथा जीवोऽप्यहंयुतः ॥ २४ ॥
Gold mixed with silver or other base metal depreciates in value. So also is the individual soul in its association with the ego.
english translation
yathaikaM ca suvarNAdi militaM rajatAdinA ॥ alpamUlyaM prajAyeta tathA jIvo'pyahaMyutaH ॥ 24 ॥
hk transliteration by Sanscript