Srimad-Bhagavatam: Canto 11 - Chapter 1 - Verse 17

Sanskrit:

हंसस्वरूप्यवददच्युत आत्मयोगंदत्त: कुमार ऋषभो भगवान् पिता न: ।विष्णु: शिवाय जगतां कलयावतीर्ण-स्तेनाहृता मधुभिदा श्रुतयोहयास्ये ॥ १७ ॥

ITRANS:

haṁsa-svarūpy avadad acyuta ātma-yogaṁdattaḥ kumāra ṛṣabho bhagavān pitā naḥviṣṇuḥ śivāya jagatāṁ kalayāvatīrṇastenāhṛtā madhu-bhidā śrutayo hayāsye

Translation:

The infallible Supreme Personality of Godhead, Viṣṇu, has descended into this world by His various partial incarnations such as Lord Haṁsa [the swan], Dattātreya, the four Kumāras and our own father, the mighty Ṛṣabhadeva. By such incarnations, the Lord teaches the science of self-realization for the benefit of the whole universe. In His appearance as Hayagrīva He killed the demon Madhu and thus brought the Vedas back from the hellish planet Pātālaloka.

Purport:

It is stated in the Skanda Purāṇa that the Lord of the universe, Hari Himself, once appeared in the form of a young brahmacārī named Kumāra and spoke transcendental knowledge to Sanat-kumāra.