Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 48
Sanskrit:
स वै बको नाम महानसुरो बकरूपधृक् ।आगत्य सहसा कृष्णं तीक्ष्णतुण्डोऽग्रसद् बली ॥ ४८ ॥
ITRANS:
sa vai bako nāma mahānasuro baka-rūpa-dhṛkāgatya sahasā kṛṣṇaṁtīkṣṇa-tuṇḍo ’grasad balī
Translation:
That great-bodied demon was named Bakāsura. He had assumed the body of a duck with a very sharp beak. Having come there, he immediately swallowed Kṛṣṇa.