CC Madhya 21.13
māyā-balasya puruṣasya kuto ’varā ye
gāyan guṇān daśa-śatānana ādi-devaḥ
śeṣo ’dhunāpi samavasyati nāsya pāram
na antam — no limit; vidāmi — know; aham — I; amī — those; munayaḥ — great saintly persons; agrajāḥ — brothers; te — of you; māyā-balasya — who has multi-energies; puruṣasya — of the Personality of Godhead; kutaḥ — how; avarāḥ — less intelligent; ye — those who; gāyan — chanting; guṇān — the qualities; daśa-śata-ānanaḥ — who has a thousand hoods; ādi-devaḥ — the Personality of Godhead; śeṣaḥ — Ananta Śeṣa; adhunā api — even until now; samavasyati — reaches; na — not; asya — of the Lord; pāram — limit.
“ ‘If I, Lord Brahmā, and your elder brothers, the great saints and sages, cannot understand the limits of the Supreme Personality of Godhead, who is full of various energies, who else can understand them? Although constantly chanting about His transcendental qualities, the thousand-hooded Lord Śeṣa has not yet reached the end of the Lord’s activities.’
This verse, spoken to Nārada Muni by Lord Brahmā, is also from Śrīmad-Bhāgavatam (2.7.41).