Shiva Purana
एतत्पंचकमेवास्य स्वरूपा वारकत्वतः ॥ पञ्चकञ्चुकमाख्यातमन्तरंगं च साधनम् ॥ ८४ ॥
This set of five is called “the five sheaths” in view of its nature of enveloping the form. It is the innermost and most essential means.
english translation
etatpaMcakamevAsya svarUpA vArakatvataH ॥ paJcakaJcukamAkhyAtamantaraMgaM ca sAdhanam ॥ 84 ॥
hk transliteration by Sanscript