SB 2.9.24
srjami tapasaivedam
grasami tapasa punah
bibharmi tapasa visvam
viryam me duscaram tapah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
I create this cosmos by such penance, I maintain it by the same energy, and I withdraw it all by the same energy. Therefore the potency is penance only.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
In executing penance, one must be determined to return home, back to Godhead, and must decide to undergo all types of tribulations for that end. Even for material prosperity and name and fame one has to undergo severe types of penances, otherwise no one can become an important figure in this material world. Why, then, should there not be severe types of penances for the perfection of devotional service? An easygoing life and attainment of perfection in transcendental realization cannot go together. The Lord is more clever than any living entity; therefore He wants to see how painstaking the devotee is in devotional service. The order is received from the Lord, either directly or through the bona fide spiritual master, and to execute that order, however painstaking, is the severe type of penance. One who follows the principle rigidly is sure to achieve success in attaining the Lord’s mercy.