Shiva Purana
॥ नन्दिकेश्वर उवाच ॥ तत्र गत्वा मुनेऽहं वै स्थित्वैकान्तस्थले सुधीः ॥ अतपं तप उग्रं सन्मुनीनामपि दुष्करम् ॥ १॥
Nandīśvara said:— O sage, after going there and staying in an isolated place with a steady mind I performed a severe penance very difficult even for good sages.
english translation
॥ nandikezvara uvAca ॥ tatra gatvA mune'haM vai sthitvaikAntasthale sudhIH ॥ atapaM tapa ugraM sanmunInAmapi duSkaram ॥ 1॥
hk transliteration by Sanscript