Exodus 30:21
They shall wash their hands and their feet, so that they will not die; it shall be a perpetual statute for them, for Aaron and his descendants throughout their generations.”
Exodus 28:43
The various articles of clothing shall be on Aaron and on his sons when they enter the Tent of Meeting, or when they approach the altar [of incense] to minister in the Holy Place, so that they do not incur guilt and die. It shall be a statute forever to Aaron and to his descendants after him.
Exodus 27:21
In the Tent of Meeting [of God with His people], outside the veil which is in front of the [ark of the] Testimony [and sets it apart], Aaron [the high priest] and his sons shall keep the lamp burning from evening to morning before the Lord. It shall be a perpetual statute [to be observed] throughout their generations on behalf of the Israelites.