Exodus 29:30, 35, 37

Seven days shall the son that is priest in his stead put them on, when he cometh into the tent of meeting to minister in the holy place.

And thus shalt thou do unto Aaron, and to his sons, according to all that I have commanded thee: seven days shalt thou consecrate them.

Seven days thou shalt make atonement for the altar, and sanctify it: and the altar shall be most holy; whatsoever toucheth the altar shall be holy.