Shiva Purana
लोकानामुपकारार्थं स्वलिंगं चाप्यकल्पयत्॥ तल्लिंगं पूजयित्वा तु सिद्धिं समधिगच्छति॥ १७॥
He has assigned his phallic form for the benefit of the worlds. The devotee attains perfection by worshipping that form.
english translation
lokAnAmupakArArthaM svaliMgaM cApyakalpayat॥ talliMgaM pUjayitvA tu siddhiM samadhigacchati॥ 17॥
hk transliteration by Sanscript