Srimad-Bhagavatam: Canto 5 - Chapter 1 - Verse 1
Sanskrit:
श्रीशुक उवाचएकदा तु महानद्यां कृताभिषेकनैयमिकावश्यको ब्रह्माक्षरमभिगृणानो मुहूर्तत्रयमुदकान्त उपविवेश ॥ १ ॥
ITRANS:
śrī-śuka uvācaekadā tu mahā-nadyāṁ kṛtābhiṣeka-naiyamikāvaśyako brahmākṣaram abhigṛṇāno muhūrta-trayam udakānta upaviveśa.
Translation:
Śrī Śukadeva Gosvāmī continued: My dear King, one day, after finishing his morning duties — evacuating, urinating and bathing — Mahārāja Bharata sat down on the bank of the river Gaṇḍakī for a few minutes and began chanting his mantra, beginning with oṁkāra.