Leviticus 16:18-19

18Then he shall go out to the altar [of burnt offering in the court] which is before the Lord and make atonement for it, and shall take some of the blood of the bull and of the goat and put it on the horns of the altar on all sides.

19With his finger he shall sprinkle some of the blood on the altar of burnt offering seven times and cleanse it and consecrate it from the uncleanness of the Israelites.