Leviticus 16:18
Then he shall come out to the altar that is before the Lord and make atonement for it. He shall take some of the bull's blood and some of the goat's blood and put it on all the horns of the altar. After the Most Holy Place and the Holy Place, Aaron moves to the burnt offering altar in the courtyard: the altar of public worship receives the atonement blood from both the bull and the goat. The mixed blood of the two sin offerings — bull (personal) and goat (communal) — is applied to all four horns of the burnt offering altar. The altar that receives the community's daily offerings throughout the year is purified on the Day of Atonement from the accumulation of inadvertent contaminations.