Shatapatha Brahmana 13.1.8.1

13.1.8.1

prajāpatiraśvamedhamasṛjata sa sṛṣṭaḥ prarcamavlīnātpra sāma taṃ vaiśvadevānyudayacanyadvaiśvadevāni juhotyaśvamedhasyaivodyatyai

Pragâpati poured forth the life-sap of the horse. When poured forth, it weighed down the rik (hymn-verse) and the sâman (hymn-tune). The Vaisvadeva (offerings) upheld that (Asvamedha): thus, when he offers the Vaisvadevas, it is for the upholding of the Asvamedha.