Śrī Nārada said: O best of the Sātvatas, you have quite correctly asked about the eternal duty of the living entity toward the Supreme Lord. Such devotional service to the Lord is so potent that its performance can purify the entire universe.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
नारद उवाच । सम्यगेतद्व्यवसितं भवता सात्वतर्षभ । यत्पृच्छसे भागवतान् धर्मांस्त्वं विश्वभावनान्
nārada uvāca | samyagetadvyavasitaṃ bhavatā sātvatarṣabha | yatpṛcchase bhāgavatān dharmāṃstvaṃ viśvabhāvanān
SB 11.2.11