Śatapatha Brāhmaṇa ("of a hundred paths") 13.1.1

He (the Adhvaryu) cooks the priests’ mess of rice: it is seed he thereby produces. Having greased a rope with the ghee which is left over, he takes it; for ghee is (a type of) fiery spirit, and the horse is sacred to Pragâpati: he thus endows Pragâpati with fiery spirit. Impure, and unfit for sacrifice, indeed, is that (animal), to wit, the horse.

The rope consists of darbha grass (poa cynosuroides);--for darbha stalks are a means of purification: he thus purifies that (horse), and immolates it as one purified and meet for sacrifice.

Now, when the horse was immolated, its seed went from it and became gold: thus, when he gives gold (to the priests) he supplies the horse with seed.

Pragâpati produced the sacrifice. His greatness departed from him, and entered the great sacrificial priests. Together with the great priests he went in search of it, and together with the great priests he found it: when the great priests eat the priests’ mess of rice, the Sacrificer thereby secures for himself the greatness of the sacrifice. Along with the priests’ mess of rice he presents gold (to the priests); for the mess of rice is seed, and gold is seed: by means of seed he thus lays seed into that (horse, and Sacrificer). It (the gold) weighs a hundred (grains); for man has a life of a hundred (years), and a hundred energies: it is life, and energy, vigour, he lays into his own self. At midday he takes Vasatîvarî water of four kinds; it is brought together from the (four) quarters, for food is in (all) the (four) quarters, and water is food: by means of food he thus secures food for him.