Leviticus 9:5-9

So they took what Moses had commanded to the front of the tent of meeting, and the whole congregation came near and stood before the Lord.

And Moses said, “This is the thing which the Lord has commanded you to do, so that the glory of the Lord may appear to you.”

Moses then said to Aaron, “Come near to the altar and offer your sin offering and your burnt offering, so that you may make atonement for yourself and for the people; then make the offering for the people, so that you may make atonement for them, just as the Lord has commanded.”

So Aaron came near to the altar and slaughtered the calf of the sin offering which was for himself.

Aaron’s sons then presented the blood to him; and he dipped his finger in the blood and put some on the horns of the altar, and poured out the rest of the blood at the base of the altar.