Śatapatha Brāhmaṇa ("of a hundred paths") 1.4.1.14

1.4.1.14

tarhi videgho māthava āsa | sarasvatyāṃ sa tata eva prāṅdahannabhīyāyemām pṛthivīṃ taṃ gotamaśca rāhūgaṇo videghaśca māthavaḥ paścāddahantamanvīyatuḥ sa imāḥ sarvā nadīratidadāha sadānīretyuttarādgirernirghāvati tāṃ haiva nātidadāha tāṃ ha sma tām purā brāhmaṇā na tarantyanatidagdhāgninā vaiśvānareṇeti

Mâthava, the Videgha, was at that time on the (river) Sarasvatî. He (Agni) thence went burning along this earth towards the east; and Gotama Râhûgana and the Videgha Mâthava followed after him as he was burning along. He burnt over (dried up) all these rivers. Now that (river), which is called 'Sadânîrâ,' flows from the northern (Himâlaya) mountain: that one he did not burn over. That one the Brâhmans did not cross in former times, thinking, 'it has not been burnt over by Agni Vaisvânara.'