Shiva Purana
मत्साम्यमेकलिंगस्य स्थापने फलमीरितम् । द्वितीये स्थापिते लिंगे मदैक्यं फलमेव हि ४५ ।
The result of installing the phallic emblem is the attainment of similarity with me. If a second phallic emblem is installed, the result is union with me.
english translation
matsAmyamekaliMgasya sthApane phalamIritam । dvitIye sthApite liMge madaikyaM phalameva hi 45 ।
hk transliteration by Sanscript