SB 7.12.20

agny-artham eva śaraṇam
 uṭajaṁ vādri-kandaram
śrayeta hima-vāyv-agni-
 varṣārkātapa-ṣāṭ svayam
Synonyms: 
agni — the fire; artham — to keep; eva — only; śaraṇam — a cottage; uṭa-jam — made of grass; — or; adri-kandaram — a cave in a mountain; śrayeta — the vānaprastha should take shelter of; hima — snow; vāyu — wind; agni — fire; varṣa — rain; arka — of the sun; ātapa — shining; ṣāṭ — enduring; svayam — personally.
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.