Leviticus 9:8-9, 18

So Aaron went to the altar and slaughtered the calf as a sin offering for himself. His sons brought him the blood, and he dipped his finger in it and put it on the horns of the altar. He poured out the rest of the blood at the base of the altar.

Then Aaron slaughtered the bull and the ram for the people’s peace offering. His sons brought him the blood, and he splattered it against all sides of the altar.