Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 5
Sanskrit:
स: लब्धसंज्ञ: पुनरुत्थितो रुषाव्यादाय केशी तरसापतद्धरिम् ।सोऽप्यस्य वक्त्रे भुजमुत्तरं स्मयन्प्रवेशयामास यथोरगं बिले ॥ ५ ॥
ITRANS:
saḥ labdha-saṁjñaḥ punar utthito ruṣāvyādāya keśī tarasāpatad dharimso ’py asya vaktre bhujam uttaraṁ smayanpraveśayām āsa yathoragaṁ bile
Translation:
Upon regaining consciousness Keśī angrily got up, opened his mouth wide and again rushed to attack Lord Kṛṣṇa. But the Lord just smiled and thrust His left arm into the horse’s mouth as easily as one would make a snake enter a hole in the ground.