Śatapatha Brāhmaṇa ("of a hundred paths") 6.6.1.1

6.6.1.1

bhūyāṃsi havīṃṣi bhavanti | agnicityāyāṃ yadu cānagnicityāyāmatīni ha karmāṇi santi yānyanyatkarmāti tānyatīni teṣāmagnicityā rājasūyo vājapeyī 'śvamedhastadyattānyanyāni karmāṇyati tasmāttānyatīni

Many are the oblations, in the building of the fire-altar, as well as at any other (special ceremony) than the building of the fire-altar. For there are supernumerary rites,--supernumerary are those which are (performed) over and above another rite: of these are the building of the altar (Agnikityâ), the Râgasûya, the Vâgapeya, and the Asvamedha; and because they are over and above the other (normal) rites, therefore they are supernumerary.