Mahabharata 3.32.35

3.32.35

kṛśāṅgāḥ suvratāścaiva tapasā dagdhakilbiṣāḥ |
prasannairmānasairyuktāḥ paśyantyetāni vai dvijāḥ || 35 ||

The gods keep up the mystery, for the illusion covering the conduct of the gods is unintelligible. Those regenerate ones that have destroyed all aspirations, that have built all their hopes on vows and asceticism, that have burnt all their sins and have acquired minds where quest and peace and holiness dwell, understand all these. Therefore, though you mayst not see the fruits of virtue, thou shouldst not yet doubt religion or gods. Thou must perform sacrifices with a will, and practise charity without insolence. Acts in this world have their fruits, and virtue also is eternal. Brahma himself told this unto his (spiritual) sons, as testified to by Kashyapa. Let thy doubt, therefore, O Krishna, be dispelled like mist. Reflecting upon all this, let thy scepticism give way to faith. Slander not God, who is the lord of all creatures. Learn how to know him. Bow down unto him. Let not thy mind be such. And, O Krishna, never disregard that Supreme Being through whose grace mortal man, by piety, acquireth immortality!'"