Shiva Purana
शिवतत्त्वमिति ख्यातं शिवार्थं जगति स्थिरम् ॥ पञ्चोपचारवद्भक्त्या पूजयेल्लिंगमुत्तमम् ॥ ३८ ॥
It is known as the Śiva-tattva and is fixed in the world for the sake of Śiva. One should worship this excellent Lingam with devotion as in the five rituals.
english translation
zivatattvamiti khyAtaM zivArthaM jagati sthiram ॥ paJcopacAravadbhaktyA pUjayelliMgamuttamam ॥ 38 ॥
hk transliteration by Sanscript