Śrīmad-Bhāgavatam · Text 10.1.16
Who is speaking and story frame
वासुदेवकथाप्रश्न: पुरुषांस्त्रीन् पुनाति हि । वक्तारं प्रच्छकं श्रोतृंस्तत्पादसलिलं यथा ॥ १६ ॥
vāsudeva-kathā-praśnaḥ
puruṣāṁs trīn punāti hi
vaktāraṁ pracchakaṁ śrotṝṁs
tat-pāda-salilaṁ yathā
The Ganges, emanating from the toe of Lord Viṣṇu, purifies the three worlds, the upper, middle and lower planetary systems. Similarly, when one asks questions about the pastimes and characteristics of Lord Vāsudeva, Kṛṣṇa, three varieties of men are purified: the speaker or preacher, he who inquires, and the people in general who listen.
Read Śrīla Prabhupāda's purport on Vedabase.io