Shatapatha Brahmana 4.3.2.5

4.3.2.5

yātayāmāni vai devaiścandāṃsi | candobhirhi devāḥ svargaṃ lokaṃ samāśnuvata mado vai pratigaro yo vā ṛci mado yaḥ sāmanraso vai sa taccandaḥsvevaitadrasaṃ dadhātyayātayāmāni karoti tairayātayāmairyajñaṃ tanvate

Now the strength of the metres was exhausted by the gods, for it was by the metres that the gods attained the world of heaven. And the response (song) is ecstasy (mada)--what ecstasy there is in the rik and that which there is in the Sâman, that is sap: this sap he now lays into the metres, and thus makes the metres of restored strength; and with them of restored strength they perform the sacrifice.