Kommentar zu Bamidbar 19:21

ומזה מי הנדה AND HE THAT SPRINKLED THE WATER OF SPRINKLING [SHALL WASH HIS GARMENTS] — Our Rabbis said that the one who sprinkles remains clean, and this statement is intended to intimate that one who bears the waters of purification becomes unclean with a more stringent uncleanness, in that he renders unclean the garments that are upon him (for it states here that he shall wash his garments), which is not so in the case of one who only touches these waters. And this fact that it here expresses it (the idea of “bearing the waters”) by the term “he that sprinkles” is only to tell you that they (the waters) do not render a person who bears them unclean unless they contain a quantity capable of being sprinkled (Yoma 14a).

ומזה מי הנדה יכבס בגדיו, “the one who administers the ash/water mixture has to wash his clothes.” Seeing that he himself is ritually pure and he administers the ash/water mixture to a ritually impure person why should he be required to immerse his clothing in a ritual bath? The reason is that in the process of sprinkling the ash/water mixture on the ritually impure person some of it may have splashed his clothing. This is what I have heard as an explanation of this halachah. However, the collective opinion of the sages in Yuma 14 is that the person concerned does not need to immerse his clothing in a ritual bath at all. The sages there understand the word מזה in our verse to mean נושא, “carries.” The reason why the Torah chooses the unusual word מזה to describe carrying is that the amount of water needed to wash the clothes in question is no larger than the amount of the ash/water mixture needed to sprinkle on the ritually impure person, just enough water as is absorbed by dipping the tips of the hyssop stalks in the mixture.

That the sprinkler is actually pure. Since it is written “the pure person shall sprinkle on the unclean person” (v. 19), but it is obvious that he was pure, for if he was impure then he would make the water impure [through contact with it]. Rather it was to teach that even though he sprinkled, he remains pure.