Shiva Purana
तस्माद्गुरुशरीरं तु गुरुलिंगं भवेद्बुधः । गुरुलिंगस्य पूजा तु गुरुशुश्रूषणं भवेत् ८६ ।
Hence the intelligent devotee shall know that the physical body of the preceptor is known as Guruliṅga the worship of which is service rendered to the preceptor.
english translation
tasmAdguruzarIraM tu guruliMgaM bhavedbudhaH । guruliMgasya pUjA tu guruzuzrUSaNaM bhavet 86 ।
hk transliteration by Sanscript