Srimad-Bhagavatam: Canto 4 - Chapter 1 - Verse 21
Sanskrit:
अत्रिणा चोदितस्तस्मै सन्दधे विशिखं रुषा ।सोऽश्वं रूपं च तद्धित्वा तस्थावन्तर्हित: स्वराट् ॥ २१ ॥
ITRANS:
atriṇā coditas tasmaisandadhe viśikhaṁ ruṣāso ’śvaṁ rūpaṁ ca tad dhitvātasthāv antarhitaḥ svarāṭ
Translation:
When the great sage Atri again gave directions, the son of King Pṛthu became very angry and placed an arrow on his bow. Upon seeing this, King Indra immediately abandoned the false dress of a sannyāsī and, giving up the horse, made himself invisible.