Numbers 19:9

והניח מחוץ למחנה AND HE SHALL LAY THEM UP WITHOUT THE CAMP — He divided it (the ashes) into three portions: one he placed on Mount Olivet, another was divided between all the priestly divisions, and the other he placed in the חיל (the space that surrounded the Temple area) (Sifrei Bamidbar 124:1; Mishnah Parah 3:11). That portion given to the priestly divisions was outside the forecourt, so that the inhabitants of the cities and anyone who required to be cleansed might take of it; as for that which was on the Mount of Olives, the High Priests purified themselves by means of it for preparing other “red cows”, whilst that which was in the space surrounding the Temple area was placed there to be kept for all times by special enactment of Scripture, as it is said, “and it shall be kept for the congregation of the children of Israel" (cf. Tosefta Parah 3 8). למי נדה FOR WATERS OF נדה — i.e. for waters of sprinkling (or casting); similar are, (Lamentations 3:53) “and they cast (וידו) a stone upon me”; (Zechariah 2:4) “to cast down (לידות) the horns of the nations”, both of which are expressions denoting “casting”. חטאת הוא IT IS A PURIFICATION FROM SIN — This, according to its literal meaning, is an expression denoting “purification”, but from the point of view of the Halachot to which it is to be subject Scripture terms it a חטאת, “sin-offering”, to state by so doing that it is similar to holy things — that it is prohibited for any other use (cf. Sifrei Bamidbar 124:2; Menachot 51b).

וְאָסַ֣ף ׀ אִ֣ישׁ טָה֗וֹר אֵ֚ת אֵ֣פֶר הַפָּרָ֔ה וְהִנִּ֛יחַ מִח֥וּץ לַֽמַּחֲנֶ֖ה בְּמָק֣וֹם טָה֑וֹר וְ֠הָיְתָ֠ה לַעֲדַ֨ת בְּנֵֽי־יִשְׂרָאֵ֧ל לְמִשְׁמֶ֛רֶת לְמֵ֥י נִדָּ֖ה חַטָּ֥את הִֽוא׃

And a man that is clean shall gather up the ashes of the heifer, and lay them outside the camp in a clean place, and it shall be kept for the congregation of the children of Yisra᾽el for the water of sprinkling: it is a purification offering.