Śatapatha Brāhmaṇa ("of a hundred paths") 1.4.1.16

1.4.1.16

tadu haitarhi | kṣetrataramiva brāhmaṇā u hi nūnamenadyajñairasiṣvadaṃtsāpi jaghanye naidāghe samivaiva kopayati tāvacītānatidagdhā hyagninā vaiśvānareṇa

Now-a-days, however, it is very cultivated, for the Brâhmans have caused (Agni) to taste it through sacrifices. Even in late summer that (river), as it were, rages along: so cold is it, not having been burnt over by Agni Vaisvânara.