Leviticus 4:30

4:30 Then the priest must take some of its blood with his finger and put it on the horns of the altar of burnt offering, and he must pour out all the rest of its blood at the base of the altar.

Leviticus 17:11

17:11 for the life of every living thing is in the blood. So I myself have assigned it to you on the altar to make atonement for your lives, for the blood makes atonement by means of the life.