Śatapatha Brāhmaṇa ("of a hundred paths") 13.3.1.4

13.3.1.4

catuṣṭoma stomo bhavati saraḍvā aśvasya sakthyābṛhattaddevāścatuṣṭomenaiva stomena pratyadadhuryaccatuṣṭoma stomo bhavatyaśvasyaiva sarvatvāya sarvastomo'tirātra uttamamaharbhavati sarvaṃ vai sarvastomo'tirātraḥ sarvamaśvamedhaḥ sarvasyāptyai sarvasyāvaruddhyai

The Katushtoma is the form of chanting (on the first day); for a bee tore out (a piece of) the horse's thigh, and by means of the Katushtoma form of chanting the gods restored it: thus when there is the Katushtoma mode of chanting, it is for the completeness of the horse. The last day is an Atirâtra with all the Stomas --with a view to his obtaining and securing everything, for an Atirâtra with all the Stomas is everything, and the Asvamedha is everything.