CC Madhya 20.262
rāmo mukundaḥ puruṣaḥ pradhānam
anvīya bhūteṣu vilakṣaṇasya
jñānasya ceśāta imau purāṇau
etau — these two, namely Rāma and Kṛṣṇa; hi — certainly; viśvasya — of the universe; ca — and; bīja-yonī — both the cause and ingredient; rāmaḥ — Balarāma; mukundaḥ — Kṛṣṇa; puruṣaḥ — the original Mahā-Viṣṇu; pradhānam — material energy; anvīya — after entering; bhūteṣu — into the material elements; vilakṣaṇasya — of varieties of manifestation; jñānasya — of knowledge; ca — also; īśāte — are the controlling power; imau — both of Them; purāṇau — are the original cause.
“ ‘Balarāma and Kṛṣṇa are the original efficient and material causes of the material world. As Mahā-Viṣṇu and the material energy, They enter into the material elements and create the diversities by multi-energies. Thus They are the cause of all causes.’
This verse is quoted from Śrīmad-Bhāgavatam (10.46.31).