Leviticus 9:9
His sons brought the blood to him, and he dipped his finger in the blood and put it on the horns of the altar; the rest of the blood he poured out at the base of the altar. Aaron applies the sin offering blood to the altar's horns with his own finger — the first time Aaron personally performs this act. His sons bring the blood; he applies it. The division of labor in the first official priestly act models the collaborative ministry that the Levitical system requires: the high priest and his sons work together in the service. The blood on the horns and the pouring at the base follow the established regulation of Leviticus 4:25 for the leader's sin offering.