Shiva Purana
महातपा दीर्घतपाः स्थविष्ठ स्थविरो ध्रुवः ॥ अहः संवत्सरो व्याप्तिः प्रमाणं परमं तपः ॥ ३७ ॥
He is a great ascetic and a long-suffering old man. The day, the year, the extent, the proof, the supreme austerity.
english translation
mahAtapA dIrghatapAH sthaviSTha sthaviro dhruvaH ॥ ahaH saMvatsaro vyAptiH pramANaM paramaM tapaH ॥ 37 ॥
hk transliteration by Sanscript