Exodus 29:9-11

And you shall wrap them with sashes, Aaron and his sons, and put the [ornamental] caps on them; and the priest’s office shall be theirs by a perpetual statute. So you shall ordain Aaron and his sons. “Then you shall bring the bull before the Tent of Meeting, and Aaron and his sons shall lay their hands on the bull’s head. Then you shall kill the bull before the LORD by the doorway of the Tent of Meeting.