Exodus 29:9-11

And you shall gird them with sashes, Aaron and his sons, and put the hats on them. The priesthood shall be theirs for a perpetual statute. So you shall consecrate Aaron and his sons. “You shall also have the bull brought before the tabernacle of meeting, and Aaron and his sons shall put their hands on the head of the bull. Then you shall kill the bull before the LORD, by the door of the tabernacle of meeting.