Srimad-Bhagavatam: Canto 7 - Chapter 1 - Verse 20
Sanskrit:
अग्न्यर्थमेव शरणमुटजं वाद्रिकन्दरम् ।श्रयेत हिमवाय्वग्निवर्षार्कातपषाट्स्वयम् ॥ २० ॥
ITRANS:
agny-artham eva śaraṇamuṭajaṁ vādri-kandaramśrayeta hima-vāyv-agni-varṣārkātapa-ṣāṭ svayam
Translation:
A vānaprastha should prepare a thatched cottage or take shelter of a cave in a mountain only to keep the sacred fire, but he should personally practice enduring snowfall, wind, fire, rain and the shining of the sun.