CC Ādi 2.56
tumi mūla nārāyaṇa — ithe ki saṁśaya
Brahmā has confirmed that Lord Kṛṣṇa is the Supreme, the source of the three manifestations known as Kṣīrodakaśāyī Viṣṇu, Garbhodakaśāyī Viṣṇu and Kāraṇodakaśāyī Viṣṇu (Mahā-Viṣṇu). For His pastimes, Lord Kṛṣṇa has four original manifestations — namely Vāsudeva, Saṅkarṣaṇa, Pradyumna and Aniruddha. The first puruṣa-avatāra, Mahā-Viṣṇu in the Causal Ocean, who is the creator of the aggregate material energy, is an expansion of Saṅkarṣaṇa; the second puruṣa, Garbhodakaśāyī Viṣṇu, is an expansion of Pradyumna; and the third puruṣa, Kṣīrodakaśāyī Viṣṇu, is an expansion of Aniruddha. All these are within the category of manifestations of Nārāyaṇa, who is a manifestation of Śrī Kṛṣṇa.