Srimad-Bhagavatam: Canto 11 - Chapter 1 - Verse 10

Sanskrit:

यस्त्वेतत् कृच्छ्रतश्चीर्णं तपो नि:श्रेयसं महत् ।कामायाल्पीयसे युञ्ज्याद् बालिश: कोऽपरस्तत: ॥ १० ॥

ITRANS:

yas tv etat kṛcchrataś cīrṇaṁtapo niḥśreyasaṁ mahatkāmāyālpīyase yuñjyādbāliśaḥ ko ’paras tataḥ

Translation:

One who with long endeavor executes this painful but exalted penance, which awards ultimate liberation, simply to achieve insignificant sense gratification must be considered the greatest fool.

Purport:

Although the process of vānaprastha described by Lord Kṛṣṇa is so glorious that even the consolation prize is promotion to Maharloka, one who consciously performs this process for such promotion to heaven is certainly the greatest fool. The Lord does not want this process to be abused or exploited by materialistic rascals, for the ultimate goal is love of Godhead.