Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 6

Sanskrit:

अथाप्लुतोऽम्भस्यमले यथाविधिक्रियाकलापं परिधाय वाससी ।चकार सन्ध्योपगमादि सत्तमोहुतानलो ब्रह्म जजाप वाग्यत: ॥ ६ ॥

ITRANS:

athāpluto ’mbhasy amale yathā-vidhikriyā-kalāpaṁ paridhāya vāsasīcakāra sandhyopagamādi sattamohutānalo brahma jajāpa vāg-yataḥ

Translation:

That most saintly of personalities would then bathe in sanctified water, dress Himself in lower and upper garments and perform the entire sequence of prescribed rituals, beginning with worship at dawn. After offering oblations into the sacred fire, Lord Kṛṣṇa would silently chant the Gāyatrī mantra.

Purport:

Śrīdhara Svāmī points out that since Lord Kṛṣṇa was in the disciplic succession from Kaṇva Muni, He offered oblations to the fire before sunrise. Then He chanted the Gāyatrī mantra.