Lord Saṅkarṣaṇa thus spoke the purport of Śrīmad-Bhāgavatam to the great sage Sanat-kumāra, who had already taken the vow of renunciation. Sanat-kumāra also, in his turn, when inquired of by Sāṅkhyāyana Muni, explained Śrīmad-Bhāgavatam as he had heard it from Saṅkarṣaṇa.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
प्रोक्तं किलैतद्भगवत्तमेन निवृत्तिधर्माभिरताय तेन । सनत्कुमाराय स चाह पृष्टः साङ्ख्यायनायाङ्ग धृतव्रताय
proktaṃ kilaitadbhagavattamena nivṛttidharmābhiratāya tena | sanatkumārāya sa cāha pṛṣṭaḥ sāṅkhyāyanāyāṅga dhṛtavratāya
SB 3.8.7