Shatapatha Brahmana 5.5.5.5

5.5.5.5

asti vā idaṃ vīryaṃ tannu te prayacāni mā tu me prahāṣīriti tasmai sāmāni prāyacattasmādapyetarhyevamevairvedairyajñaṃ tanvate yajurbhirevāgre 'thargbhiratha sāmabhirevaṃ hyasmā etatprāyacat

'There is here a (source of) strength: I will give that up to thee; but do not smite me!' and gave up to him the Sâman-hymns (or tunes). Therefore they spread the sacrifice even to this day in the same way with those (three) Vedas, first with the Yagus-formulas, then with the Rik-verses, and then with the Sâman-hymns; for thus he (Vritra) at that time gave them up to him.