Ezekiel 43:20

43:20 You will take some of its blood, and place it on the four horns of the altar, on the four corners of the ledge, and on the border all around; you will cleanse it and make atonement for it.

Ezekiel 43:26

43:26 For seven days they will make atonement for the altar and cleanse it, so they will consecrate it.