Sri Sri Dasavatara Stotra

Śrīla Jayadeva Gosvāmī has offered his prayer to the ten avatāra, principal avatāra. Keśava dhṛta-mīna-śarīra jaya jagadīśa hare.

pralaya-payodhi-jale dhṛtavān asi vedaṁ
vihita-vahitra-caritram akhedam
keśava dhṛta-mīna-śarīra jaya jagadīśa hare
(Śrī Daśāvatāra Stotra)

Similarly, tortoise avatāra, Kūrma avatāra, Varāha avatāra. Nṛsiṁha-deva:

tava kara-kamala-vare nakham adbhuta-śṛṅgaṁ
dalita-hiraṇyakaśipu-tanu-bhṛṅgam
keśava dhṛta-narahari-rūpa jaya jagadīśa hare
(Śrī Daśāvatāra Stotra)

Similarly, Vāmana avatāra.
So origin of all these avatāra is the Saṅkarṣaṇa, this Saṅkarṣaṇa. Advaitam acyutam anādim ananta-rūpam ādyaṁ purāṇa-puruṣaṁ nava-yauvanam (Bs. 5.33). Kṛṣṇa is the ādyam. Purāṇa-puruṣam, the origin. Ahaṁ sarvasya prabhavaḥ (BG 10.8). In the Bhagavad-gītā it is said, ahaṁ sarvasya prabhavaḥ. All the avatāras . . . Kṛṣṇa is avatārī, the source of all avatāras. There are ananta, unlimited number of incarnation, constantly coming like the waves of the river or the sea, but the original person is Kṛṣṇa. So Kṛṣṇa says, confirms it, that ahaṁ sarvasya prabhavo mattaḥ sarvaṁ pravartate: “All avatāras, everything, is all emanations from Me.” So iti matvā bhajante māṁ budhā bhāva-samanvitāḥ (BG 10.8). So if we simply worship Kṛṣṇa—Kṛṣṇa also demands that, mām ekam—then all the avatāras, all the demigods, everything, is worshiped.
(750102 – Lecture SB 03.26.25 – Bombay)