Leviticus 9:7-9

⁷And Mosheh said to Aharon, Approach the altar, and make thy sin offering and thy burnt sacrifice, and make atonement for thyself and for the people, and perform the oblation of the people, and make atonement for them, as the Lord commanded.

⁸And Aharon drew near to the altar, and slew the calf for the sin offering for himself.

⁹And the sons of Aharon brought the blood to him, and he dipped his finger in the blood, and put it upon the horns of the altar, and poured out the blood at the base of the altar.