Exodus 40:31 - John Gill's Exposition of the Entire Bible

And Moses, and Aaron, and his sons, washed their hands and their feet thereat. This laver was for the priests, and Moses, officiating as a priest, washed in it, with Aaron, and his sons, whom he was now about to consecrate to the priest's office, and invest with it by offering sacrifice for them; Jarchi says this was on the eighth day of the consecration.