Srimad-Bhagavatam: Canto 8 - Chapter 1 - Verse 15

Sanskrit:

तमात्मनोऽनुग्रहार्थं प्रीत्या मत्स्यवपुर्धरम् ।अजानन् रक्षणार्थाय शफर्या: स मनो दधे ॥ १५ ॥

ITRANS:

tam ātmano ’nugrahārthaṁprītyā matsya-vapur-dharamajānan rakṣaṇārthāyaśapharyāḥ sa mano dadhe

Translation:

To please himself, King Satyavrata, not knowing that the fish was the Supreme Personality of Godhead, decided with great pleasure to give the fish protection.

Purport:

Here is an example of giving service to the Supreme Personality of Godhead even without knowledge. Such service is called ajñāta-sukṛti. King Satyavrata wanted to show his own mercy, not knowing that the fish was Lord Viṣṇu. By such unknowing devotional service, one is favored by the Supreme Personality of Godhead. Service rendered to the Supreme Lord, knowingly or unknowingly, never goes in vain.