Shiva Purana
एवमादित्यवारे हि पूजा जन्मनिवर्तिका । आदिवारे महालिंगं प्रणवेनैव पूजयेत् 1-16-११० ।
The worship thus performed on Sundays wards off births. The devotee shall worship the great phallic emblem on Sundays with the syllable Om.
english translation
evamAdityavAre hi pUjA janmanivartikA । AdivAre mahAliMgaM praNavenaiva pUjayet 1-16-110 ।
hk transliteration by Sanscript