SB 10.70.6
athapluto ’mbhasy amale yatha-vidhi
kriya-kalapam paridhaya vasasi
cakara sandhyopagamadi sattamo
hutanalo brahma jajapa vag-yatah
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 Krsna would silently chant the Gayatri mantra.
Purport:
Sridhara Svami points out that since Lord Krsna was in the disciplic succession from Kanva Muni, He offered oblations to the fire before sunrise. Then He chanted the Gayatri mantra.