Śrīmad-Bhāgavatam · Text 2.7.5
Who is speaking and story frame
तप्तं तपो विविधलोकसिसृक्षया मे
आदौ सनात् स्वतपस: स चतु:सनोऽभूत् ।
प्राक्कल्पसम्प्लवविनष्टमिहात्मतत्त्वं
सम्यग् जगाद मुनयो यदचक्षतात्मन् ॥ ५ ॥
taptaṁ tapo vividha-loka-sisṛkṣayā me
ādau sanāt sva-tapasaḥ sa catuḥ-sano ’bhūt
prāk-kalpa-samplava-vinaṣṭam ihātma-tattvaṁ
samyag jagāda munayo yad acakṣatātman
To create different planetary systems I had to undergo austerities and penance, and the Lord, thus being pleased with me, incarnated in four sanas [Sanaka, Sanatkumāra, Sanandana and Sanātana]. In the previous creation the spiritual truth was devastated, but the four sanas explained it so nicely that the truth at once became clearly perceived by the sages.
Read Śrīla Prabhupāda's purport on Vedabase.io