Rashi on Numbers 5:2/רש"י על במדבר ה׳:ב׳

1צו את בני ישראל וגו׳ COMMAND THE CHILDREN OF ISRAEL etc. — This section was spoken on the day when the Tabernacle was erected; there were eight sections spoken on that day, as is related in Treatise Gittin 60a, in the chapter beginning with the word הנזקין.

2וישלחו מן המחנה [COMMAND THE CHILDREN OF ISRAEL] THAT THEY SEND AWAY FROM THE CAMP [EVERY LEPER etc.] — There were three camps one within the other whenever they encamped: the area within the hangings was the “camp of the Shechinah”, the encampment of the Levites round about this, as is described in the Sedrah במדבר סיני (Numbers 1:53), was the “camp of the Levites”, and from there outward up to the end of the encampment of the divisions in all the four directions was the “camp of the Israelites”. The leper was sent out from all of them; the person suffering from a flux was allowed to stay in the “camp of the Israelites”, but was sent out from the two inner camps, whilst a person who had become unclean by reason of a corpse was allowed to stay in the “camp of the Levites” also, and was sent out only from that of the Shechinah. All this have our Rabbis deduced in Treatise Pesachim 67a from the verses of our text.

3טמא לנפש — Onkelos translates this by דמסאב לטמי נפשא דאנשא. I say that it (the word טמי in this rendering) is an expression in Aramaic for human bones, so that the Targum means: “whosoever is unclean by reason of the bones of a human being’’. There are many examples of the use of this word in Genesis Rabbah, as e.g. (Genesis Rabbah 78:1): Hadrian, שחיק טמיא, which means, “Hadrian may his bones be crushed!”