Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 23
Sanskrit:
सोऽतिवीर्योऽसुरो राम हे कृष्ण खररूपधृक् ।आत्मतुल्यबलैरन्यैर्ज्ञातिभिर्बहुभिर्वृत: ॥ २३ ॥
ITRANS:
so ’ti-vīryo ’suro rāmahe kṛṣṇa khara-rūpa-dhṛkātma-tulya-balair anyairjñātibhir bahubhir vṛtaḥ
Translation:
O Rāma, O Kṛṣṇa! Dhenuka is a most powerful demon and has assumed the form of an ass. He is surrounded by many friends who have assumed a similar shape and who are just as powerful as he.