Midrash su Numeri 19:19

Rabbi Yehuda opened in the name of Rabbi Shimon ben Pazi, "'Listen my son and take my words' (Proverbs 4:10). Many takings have I commanded you in order to give you merit. I said to you (Numbers 19:2), 'and you will take to you a pure red cow.' [Was it] maybe for My sake? But rather it was for your sake, to purify you, as it is written (Numbers 19:19), 'And the pure one will sprinkle on the impure one.' I said to you (Exodus 25:2), 'and they shall take an offering for Me' in order that I will dwell among you: 'And make for Me a sanctuary' (Ibid., verse 8). As if it were possible, the Holy One, blessed be He, said, 'take Me and I will dwell among you' - it does not say, 'and they shall take an offering,' but rather, 'and they shall take (for) Me:' they are taking Me. I said to you (Leviticus 24:2), 'and they shall take to you pure olive oil.' And do I need your light - behold, it is written (Daniel 2:22), 'and light dwells with Him?' But rather to give you merit and to atone for your souls which is compared to a candle, as it is stated (Proverbs 20:27), 'The candle of God is the soul of a man, it searches all of the chambers of the innards.' And now that I have said to you, 'And you shall take for yourselves on the first day,' it is to give you merit, so that I will bring down the rain for you. Hence Moshe warned Israel, 'And you shall take for yourselves on the first day.'"

(Bamidbar 19:19) "And the clean one shall sprinkle on the unclean one": If the clean one sprinkles upon the unclean one, he becomes unclean. These are the words of R. Akiva. The sages say: Scripture is speaking only of those things which have become unclean (as being sprinkled upon, and not of things which are clean.) "on the third day and on the seventh day": Scripture comes to teach us that one who has become tamei through a dead body requires sprinkling on the third and seventh days. You say it comes to this end, but perhaps the intent is that if he sprinkled on the third day he becomes clean on the seventh day, and if not, not? It is, therefore, written "and he shall cleanse him on the seventh day." It repeats ("on the seventh day") to indicate that it is invalid otherwise (i.e., if he does not sprinkle on the seventh day.) "and he shall wash his garments and he shall bathe in water": This tells me (that he may wash his garments) only on the seventh day. Whence do I derive (that it is also permissible on) the eighth and ninth days? From "and he shall cleanse him on the seventh day," followed by "and he shall wash his garments and bathe in water and he will be clean in the evening."

(Bamidbar 31:24) "And you shall wash your garments on the seventh day and you shall be clean": What is the intent of this? Since we are speaking of one slain by the sword, Scripture comes to teach us that the sword and one who touches it is tamei for seven days. Whence do we derive (the same for transfer of tumah from) vessels (i.e., appurtenances) to man to vessels (appurtenances)? From "And you shall wash your garments." "and then you shall come to the camp." Just as here, (without washing of garments and sprinkling) he is forbidden to enter the camp (of the Shechinah), so, there (vis-à-vis the red heifer, Vayikra 19:19) he is forbidden to enter the camp; and just as there, until the evening, so, here, until the evening.