Numbers 19:4

And Eleazar the priest shall take of her blood... — The appointed rites were to be discharged by Eleazar, not by Aaron, who would otherwise have been temporarily disqualified by legal impurity from the discharge of his high-priestly functions.

Before the tabernacle of the congregation... — i.e., opposite to the entrance of the Tabernacle, but, as stated in the preceding verse, outside the camp, because the act had reference to the uncleanness of death.