Srimad Bhagavatam Canto 11, Chapter 18, Text 04

SB 11.18.4

grisme tapyeta pañcagnin
 varsasv asara-sad jale
akantha-magnah sisira
 evam vrttas tapas caret
 
Translation: 
 
Thus engaged as a vanaprastha, one should execute penance during the hottest summer days by subjecting oneself to burning fires on four sides and the blazing sun overhead; during the rainy season one should remain outside, subjecting oneself to torrents of rain; and in the freezing winter one should remain submerged in water up to one’s neck.
 
Purport: 
 
One who engages in sense gratification must perform severe penances at the end of life to counteract his sinful, hedonistic activities. A devotee of the Lord, however, naturally develops Krsna consciousness and need not subject himself to such radical penances. As stated in the Pañcaratra:
 
aradhito yadi haris tapasa tatah kim
 naradhito yadi haris tapasa tatah kim
antar bahir yadi haris tapasa tatah kim
 nantar bahir yadi haris tapasa tatah kim
 
“If one is worshiping the Lord properly, what is the use of severe penances? And if one is not properly worshiping the Lord, what is the use of severe penances? If Sri Krsna is realized within and without everything that exists, what is the use of severe penances? And if Sri Krsna is not seen within and without everything, then what is the use of severe penances?”
Srimad Bhagavatam Canto 11, Chapter 18, Text 03
Srimad Bhagavatam Canto 11, Chapter 18, Text 05