Śatapatha Brāhmaṇa ("of a hundred paths") 13.3.5

Verily, there are deaths connected with all the worlds; and were he not to offer oblations to them, Death would get hold of him in every world: when he offers oblations to the Deaths, he wards off Death in every world.

Concerning this they say, 'If, in offering, he were to name them all, saying, "To such (a death) hail! To such (a death) hail!" he would make that manifold death his enemy, and would give himself over to Death.' Only one oblation he offers to one of them, with, 'To Death, hail!' for there is indeed but one Death in yonder world, even Hunger: it is him he wards off in yonder world.

A second oblation he makes with, 'To Brahman-slaying, hail!' for, doubtless, a murder other than the slaying of a Brahman is no murder; but that--to wit, the slaying of a Brahman--is manifestly murder: he thus manifestly wards off Death.

Mundibha Audanya it was who discovered this atonement for the slaying of a Brahman; and when one offers the oblation to the Brahmahatyâ he prepares a remedy for the slayer of a Brahman by satisfying Death himself with an oblation, and making a protection for him (the slayer). At whosoever's Asvamedha, therefore, this oblation is offered, even if in after-times any one in his family kills a Brahman, he thereby prepares a remedy (expiation) for him.