Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 16
Sanskrit:
इति व्यवस्याजगरं बृहद् वपु:स योजनायाममहाद्रिपीवरम् ।धृत्वाद्भुतं व्यात्तगुहाननं तदापथि व्यशेत ग्रसनाशया खल: ॥ १६ ॥
ITRANS:
iti vyavasyājagaraṁ bṛhad vapuḥsa yojanāyāma-mahādri-pīvaramdhṛtvādbhutaṁ vyātta-guhānanaṁ tadāpathi vyaśeta grasanāśayā khalaḥ
Translation:
After thus deciding, that crooked Aghāsura assumed the form of a huge python, as thick as a big mountain and as long as eight miles. Having assumed this wonderful python’s body, he spread his mouth like a big cave in the mountains and lay down on the road, expecting to swallow Kṛṣṇa and His associates the cowherd boys.