Ksirodakasayi Visnu is the Supersoul of all living entities and the maintainer of all the universes. Sesa Naga is His further subpart - CC Adi 5.109

Expressions researched:
"Ksirodakasayi Visnu is the Supersoul of all living entities and the maintainer of all the universes. Sesa Naga is His further subpart"

CC Adi-lila

I offer my respectful obeisances unto the feet of Śrī Nityānanda Rāma, whose secondary part is the Viṣṇu lying in the ocean of milk. That Kṣīrodakaśāyī Viṣṇu is the Supersoul of all living entities and the maintainer of all the universes. Śeṣa Nāga is His further subpart.

CC Adi 5.109, Translation:

I offer my respectful obeisances unto the feet of Śrī Nityānanda Rāma, whose secondary part is the Viṣṇu lying in the ocean of milk. That Kṣīrodakaśāyī Viṣṇu is the Supersoul of all living entities and the maintainer of all the universes. Śeṣa Nāga is His further subpart.