YV 3.5n

The Horse Sacrifice (continued) The eye of Prajapati swelled, that fell away, that became a horse; because it swelled (áçvayat), that is the reason why the horse (áçva) has its name. By the horse sacrifice the gods replaced it. He who sacrifices with the horse sacrifice makes Prajapati whole; verily he becomes whole; this is the atonement for everything, and the cure for everything. All evil by it the gods overcame; by it also the gods overcame (the sins of) Brahman- slaying; all evil [1] he overcomes, he overcomes Brahman-slaying who sacrifices with the horse sacrifice, and he who knows it thus. It was the left eye of Prajapati that swelled; therefore they cut off from the horse on the left side, on the right from other animals. The mat is of reeds; the horse has its birthplace in the waters, the reed is born in the waters; verily he establishes it in its own birthplace. The Stoma is the fourfold one; the bee tore the thigh of the horse, the gods made it whole with the fourfold Stoma; in that there is the fourfold Stoma, (it is) to make whole the horse.