Мидраш к Бамидбар 19:12

2) (The verse is needed for the above, for without it we would say) Does it not follow a fortiori that he does require seven sprinklings, viz.: If a leper, who does not require sprinkling on the third and seventh day (viz. Bamidbar 19:12) requires seven sprinklings, then one who is tamei through a dead body, who does require sprinkling on the third and seventh day — how much more so does he require seven sprinklings! It must, therefore, be written "And he shall sprinkle upon the one to be cleansed from the leprosy." The one to be cleansed from the leprosy requires seven sprinklings; one (who is to be cleansed from) dead body uncleanliness does not require seven sprinklings.

"they shall take a heifer" ("eglath bakar"): R. Eliezer says: "eglath" — (up to) one year old; "parah" (a cow, the parah adumah [viz. Bamidbar 19:12]) — two years old. The sages say: "eglah" — (even one that is) two years old; "parah" — three or four years old — it being written (in respect to the former) "eglath bakar." How is this to be implemented? A two-year old satisfies both, "eglah" and "bakar." Similarly, (Ibid. 5) "Then there shall draw near the Cohanim … (6) and all the elders of that city." How so? The elders for washing; the Cohanim for atonement.