מדרש על במדבר 19:18

(Bamidbar 19:18) "And a clean man shall take": "Taking" is written here, and elsewhere (Ibid. 5) "Just as taking there involves three (objects), so, "taking" here. "hyssop": and not Greek hyssop, and not Kochalith hyssop, and not Roman hyssop, and not desert hyssop — and not any hyssop designated by an epithet.

(Bamidbar 19:18) "and a clean man shall dip (it) in the water": There must be enough water for "dipping" (three calyxes). "a man": to exclude a minor. This would exclude both a minor and a woman. It is, therefore, written "clean" — to include a woman. These are the words of R. Yishmael. R. Akiva says: Why is "clean" written? Even if it were not written, I would know it a fortiori, viz.: If the gatherer must be clean (viz. Ibid. 9), how much more so the sprinkler! What, then, is the intent of "clean"? Clean of all tumah. And who is he (who is not clean of all tumah)? One who immersed in the daytime. R. Akiva says: It is written here "clean," and, elsewhere, (Ibid. 9), "clean." Just as (one who is) "clean" here is tamei vis-à-vis (the bringing of) a sin-offering, so, (one who is) "clean" there. "and he shall sprinkle it upon the tent." Scripture here apprises us that a tent is susceptible of tumah. Variantly: Scripture apprises us (that only those vessels require sprinkling, which were there) when the tent became tamei, (but not those which were brought in after the body was removed.) "and he shall sprinkle it … and upon him who touched a bone" — a bone the size of a barley-corn. You say this, but perhaps ever min hechai (a limb torn from a living person) is intended? (Ibid. 16) "or the bone of a man" already speaks of ever min hechai." What, then, is the intent of "and upon him who touched a bone"? A bone the size of a barley-corn. "or a slain one or a dead body or a grave": Just as all are mentioned vis-à-vis tumah (Ibid. 16), so, all are mentioned vis-à-vis sprinkling (here).