Leviticus 9:7-10

Moses said to Aaron, “Come to the altar and sacrifice your sin offering and your burnt offering and make atonement for yourself and the people; sacrifice the offering that is for the people and make atonement for them, as the LORD has commanded.” So Aaron came to the altar and slaughtered the calf as a sin offering for himself. His sons brought the blood to him, and he dipped his finger into 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. On the altar he burned the fat, the kidneys and the long lobe of the liver from the sin offering, as the LORD commanded Moses