Śatapatha Brāhmaṇa ("of a hundred paths") 13.3.6

When the horse was slaughtered, the life-sap went out of it; it became the Asvastomîya (set of oblations): when he offers the Asvastomîya (oblations) he indeed supplies the horse with life-sap.

He performs it with ghee; for ghee is life-sap, and the Asvastomîya is life-sap: by means of life-sap he thus puts life-sap into it. He performs with ghee, for that--to wit, ghee--is the favourite resource of the gods: he thus supplies them with their favourite resource.

Having performed the Asvastomîya (set of) oblations, he offers the Dvipadâs; for the Asvastomîya is the horse, and the Dvipadâ is man, for man is two-footed (dvipâd), supported on two (feet): he thus supplies him with a support.

Concerning this they say, 'Is the Asvastomîya to be offered first, or the Dvipadâ?' The Asvastomîya, surely, is cattle, and the Dvipadâ is man: inasmuch as he performs the Dvipadâs after performing the Asvastomîya, man subsequently establishes himself amongst cattle.

Sixteen Asvastomîya oblations he performs, for animals (cattle) consist of sixteen parts: that is the measure of cattle, and he thus supplies cattle with their (right) measure; Were he to offer either less or more, he would deprive cattle of their (right) measure. Sixteen he offers, for cattle consist of sixteen parts: that is the measure of cattle, and he thus supplies cattle with their (right) measure. He offers no other as a final oblation: were he to offer another as a final oblation, he would lose his support. The Dvipadâs he offers last, for Dvipadâs are a support: he thus finds a support (establishes himself). With, 'To Gumbaka hail!' he offers, at the purificatory bath, the last oblation; for Gumbaka is Varuna: by sacrifice he thus manifestly redeems himself from Varuna. He offers it on the head of a white-spotted, baldheaded (man) with protruding teeth and reddish brown eyes; for that is Varuna's form: by (that) form (of his) he thus redeems himself from Varuna.

Having stepped out (of the water) he prepares twelve messes of cooked rice for the priests, or performs twelve ishtis. Concerning this they say, 'These to wit, ishtis--are a form of sacrifice: were he to perform ishtis, the sacrifice would be ready to incline towards him; but he would become the worse for it, for, surely, of exhausted strength now are the metres (offering formulas) of him who has performed the Soma-sacrifice;--how could he make use of them so soon? For when the sacrifice is complete, Vâk (speech and sacred writ) is wholly gained, and, being gained, it now is exhausted in strength, and, as it were, wounded and mangled; but sacrifice is speech: hence he should not make use of it.'

Having stepped out (of the water) he should certainly prepare twelve messes of rice for the priests; for cooked rice is Pragâpati, and Pragâpati is the year, Pragâpati is the sacrifice: it is the year, the sacrifice, he thus gains, and the sacrifice becomes ready to incline towards him, and he does not become the worse for it.