Shiva Purana
अथवा मानुषे लिंगेप्यार्षे दैवे स्वयंभुवि । स्थापितेऽपूर्वके लिंगे सोपचारं यथा तथा 1-11-३० ।
Or he shall perform all the sixteen rites in the phallic emblem of human, saintly or godly origin, or in one naturally risen up (Svayambhū) or in one of very extraordinary nature installed duly.
english translation
athavA mAnuSe liMgepyArSe daive svayaMbhuvi । sthApite'pUrvake liMge sopacAraM yathA tathA 1-11-30 ।
hk transliteration by Sanscript