Shiva Purana
देवन्नित्यमशक्तश्चेत्पूजितुं गुरुणा शुभम् ॥ स्फाटिकं पीठिकोपेतं गृह्णीयाल्लिंगमैश्वरम् ॥ ९३॥
If he cannot worship the deity worshipped by his preceptor he shall take up Śivaliṅga of crystal along with the pedestal.
english translation
devannityamazaktazcetpUjituM guruNA zubham ॥ sphATikaM pIThikopetaM gRhNIyAlliMgamaizvaram ॥ 93॥
hk transliteration by Sanscript