Midras Imamat 10:7: Sifra & Bereshit Rabbah

28) (Vayikra 10:6): "And Moses said to Aaron and to Elazar and to Ithamar, his sons: Your hair do not grow long … (Vayikra 10:7) and from the door of the tent of meeting do not go out.": From here they ruled: Those who were executed by beth-din are not to be attended upon for any purpose. "and from the door of the tent of meeting do not go out": From here they ruled: If a high-priest lost one of his kin, he does not follow the litter. When they (the members of the funeral cortege) are concealed (from his sight), he may reveal himself. When they are revealed, he must conceal himself. Lest you say: We shall go to our houses and mourn and grieve and wail, has the L–rd not commanded us not to leave the sanctuary? (Vayikra 10:6): "And let your brethren, the entire house of Israel, mourn the burning that the L–rd has burned … (Vayikra 10:7): and they did according to the word of Moses": They vindicated G d's judgment upon them and they were silent.

42) (Vayikra 10:7): "And from the door of the tent of meeting you shall not go out": I might think (that they shall not go out) whether or not they are officiating; it is, therefore, written (Vayikra 21:12): "and he shall not go out (to follow the litter) and he will not profane (the sanctuary of his G d") [by serving while he is an onein (a mourner)]. When is it that he does not go out and does not profane? When he is officiating. Here, too, "you shall not go out" (speaks of an instance) when he is officiating. (Vayikra 10:7) "lest you die": The negative implies the positive (if you do go out).

43) "for the anointing oil of the L–rd is upon you": What is the intent of this? I might think that only Aaron and his sons who were exalted with the oil of anointment, if they went out while officiating, would be liable to death — it is, therefore, written "for the anointing oil of the L–rd is upon you" (upon all high-priests, even if not anointed). "and they did according to the word of Moses": They fulfilled in themselves the mitzvah of Moses their teacher. And thus does Scripture praise Israel in the section of the sending (out of the camp) those who had become tamei, viz. (Bamidbar 5:4): "And the children of Israel did so, and they sent them outside the camp." And thus does Scripture praise Joshua, viz. (Joshua 11:15): "As the L–rd had commanded Moses, so had Moses commanded Joshua, and so did Joshua do."