Halacha

הלכה א
מַעֲלוֹת יְתֵרוֹת עָשׂוּ בְּטָהֳרַת פָּרָה אֲדֻמָּה וְהַרְחָקוֹת גְּדוֹלוֹת הִרְחִיקוּ מִטֻּמְאַת הַמֵּת בְּכָל מַעֲשֶׂיהָ. מִפְּנֵי שֶׁהִיא כְּשֵׁרָה בִּטְבוּלֵי יוֹם חָשׁוּ שֶׁמָּא יָבוֹאוּ לְזַלְזֵל בָּהּ. וּמִפְּנֵי זֶה כְּשֶׁמַּפְרִישִׁין הַכֹּהֵן הַשּׂוֹרֵף אוֹתָהּ מַפְרִישִׁין אוֹתוֹ לְלִשְׁכָּה מוּכֶנֶת בָּעֲזָרָה. וּבֵית אֶבֶן הָיְתָה נִקְרֵאת מִפְּנֵי שֶׁכָּל כֵּלֶיהָ כְּלֵי אֲבָנִים שֶׁאֵין מְקַבְּלִין טֻמְאָה. וּבִכְלֵי הָאֶבֶן הָיָה מִשְׁתַּמֵּשׁ כָּל שִׁבְעַת יְמֵי הַהַפְרָשָׁה. וְלֹא הָיוּ נוֹגְעִין בּוֹ אֶחָיו הַכֹּהֲנִים כְּדֵי לְהַרְבּוֹת בְּטָהֳרָתוֹ:
כסף משנה
1.
Extra stringencies were employed with regard to the purity observed in preparation for offering the red heifer and great extremes were taken to keep a distance from the ritual impurity associated with a human corpse in all the activities associated with its offering. The rationale is that since it is acceptable for a person who immersed that day to bring it, our Sages were concerned that people would treat this offering with disdain.
For this reason, when the priest who burns it is isolated, he is isolated to a prepared chamber in the Temple Courtyard. It was called the House of Stone, because all of the utensils in it were stone utensils that do not contract impurity. He would use the stone utensils throughout the seven days that he is isolated. His priestly brethren would not touch him in order to increase his purity.

הלכה ב
שִׁבְעַת יָמִים קדֶם שְׂרֵפַת הַפָּרָה מַפְרִישִׁין כֹּהֵן הַשּׂוֹרֵף אוֹתָהּ מִבֵּיתוֹ. כְּשֵׁם שֶׁמַּפְרִישִׁין כֹּהֵן גָּדוֹל לַעֲבוֹדַת יוֹם הַכִּפּוּרִים. וְדָבָר זֶה קַבָּלָה מִמּשֶׁה רַבֵּנוּ. וְכֵן מַפְרִישִׁין אוֹתוֹ מֵאִשְׁתּוֹ שֶׁמָּא תִּמָּצֵא נִדָּה וְיִהְיֶה טָמֵא שִׁבְעַת יָמִים:
כסף משנה
2.
For seven days before the burning of the red heifer, the priest who would burn it is isolated from his home, just like the High Priest is isolated for the sake of the service of Yom Kippur. This was received as part of the Oral Tradition from Moses. Similarly, he is isolated from his wife, lest it be discovered that she was a nidah and he be impure for seven days.

הלכה ג
הַלִּשְׁכָּה שֶׁהָיָה יוֹשֵׁב בָּהּ כָּל שִׁבְעָה צְפוֹנִית מִזְרָחִית הָיְתָה. כְּדֵי לְהַזְכִּירוֹ שֶׁהִיא כְּחַטָּאת הַנִּשְׁחֶטֶת בַּצָּפוֹן אַף עַל פִּי שֶׁהִיא נִשְׁחֶטֶת בַּחוּץ:
כסף משנה
3.
The chamber in which this priest would abide for all these seven days was in the northeast portion of the Temple Courtyard. It was positioned there to remind the priest that the red heifer is like a sin-offering that is slaughtered in the northern portion of the Temple Courtyard, even though the red heifer is slaughtered outside the Temple.

הלכה ד
כָּל יוֹם וְיוֹם מִשִּׁבְעַת יְמֵי הַהַפְרָשָׁה מַזִּין עָלָיו מֵי חַטָּאת. שֶׁמָּא נִטְמָא לְמֵת וְהוּא לֹא יָדַע. חוּץ מִיּוֹם רְבִיעִי לְהַפְרָשָׁה שֶׁאֵין צָרִיךְ הַזָּאָה לְפִי שֶׁאִי אֶפְשָׁר שֶׁלֹּא יִהְיֶה לֹא שְׁלִישִׁי לְטֻמְאָתוֹ וְלֹא שְׁבִיעִי. שֶׁאֵין הַזָּאָה בַּשְּׁבִיעִי עוֹלָה מִשּׁוּם הַזָּאַת שְׁבִיעִי עַד שֶׁיַּזֶּה בַּשְּׁלִישִׁי מִלְּפָנֶיהָ. וּמִן הַדִּין הָיָה שֶׁאֵין צָרִיךְ הַזָּאָה אֶלָּא בִּשְׁלִישִׁי וּשְׁבִיעִי לְהַפְרָשָׁה בִּלְבַד וְזֶה שֶׁמַּזִּין יוֹם אַחַר יוֹם מַעֲלָה יְתֵרָה עָשׂוּ בְּפָרָה:
כסף משנה
4.
On every one of the seven days of his isolation, water with the ashes of the red heifer should be sprinkled upon him lest he unknowingly have contracted impurity due to contact with a corpse with the exception of the fourth day of his isolation. That day does not require sprinkling. The rationale is that it is impossible for it to be the third day of his impurity or the seventh day of his impurity. For the sprinkling of the ashes on the seventh day is not considered as the sprinkling of the seventh day unless the ashes were sprinkled on the third day before it. According to law, there is no need to sprinkle the ashes upon him on any days other than the third and the seventh days of isolation. The sprinkling day after day is an extra stringency enacted with regard to the red heifer.

הלכה ה
בִּרְבִיעִי בְּשַׁבָּת הָיוּ מַפְרִישִׁין אוֹתוֹ כְּדֵי שֶׁיָּחוּל רְבִיעִי שֶׁלּוֹ לִהְיוֹת בְּשַׁבָּת. שֶׁהַהַזָּיָה אֵינָהּ דּוֹחָה שַׁבָּת וְהָרְבִיעִי אֵין צָרִיךְ הַזָּיָה:
כסף משנה
5.
He would be isolated on Wednesday, so that the fourth day of his isolation would fall on the Sabbath, for the sprinkling of the ashes of the red heifer does not supersede the Sabbath prohibitions, and the fourth day does not require the sprinkling of the ashes.

הלכה ו
בְּכָל יוֹם וְיוֹם מִימֵי הַהַפְרָשָׁה שֶׁמַּזִּין עָלָיו בָּהֶם. מַזִּין מֵאֵפֶר פָּרָה מִן הַפָּרוֹת שֶׁנִּשְׂרְפוּ כְּבָר. וְאִם לֹא הָיָה שָׁם אֶלָּא אֵפֶר פָּרָה אַחַת בִּלְבַד מַזִּין מִמֶּנּוּ עָלָיו כָּל הַשִּׁשָּׁה:
כסף משנה
6.
On all the days of his isolation when the ashes of the red heifer are sprinkled upon him, the ashes of all the red heifers that were burnt previously were sprinkled on him. If, however, there were only ashes from one red heifer, those ashes are used for all six days.

הלכה ז
כְּשֶׁמַּזִּין עָלָיו בִּימֵי הַהַפְרָשָׁה אֵין מַזֶּה עָלָיו אֶלָּא אָדָם שֶׁלֹּא נִטְמָא בְּמֵת מֵעוֹלָם שֶׁהַמַּזֶה צָרִיךְ שֶׁיִּהְיֶה טָהוֹר. וְאִם תֹּאמַר יַזֶּה עָלָיו אִישׁ שֶׁנִּטְמָא וְהֻזָּה עָלָיו. שֶׁמָּא זֶה שֶׁהִזָּה עָלָיו לֹא הָיָה טָהוֹר מִטֻּמְאַת מֵת. וְכֵן הַכֵּלִים שֶׁמְּמַלְּאִין בָּהֶן וּמְקַדְּשִׁין לְהַזּוֹת עַל הַכֹּהֵן הַשּׂוֹרֵף כֻּלָּם כְּלֵי אֲבָנִים הָיוּ שֶׁאֵין מְקַבְּלִין טֻמְאָה. וְכָל אֵלּוּ הַדְּבָרִים מַעֲלוֹת יְתֵרוֹת הֵן שֶׁעָשׂוּ בָּהּ. וְכֵיצַד יִמָּצֵא אִישׁ שֶׁלֹּא נִטְמָא בְּמֵת מֵעוֹלָם. חֲצֵרוֹת הָיוּ בִּירוּשָׁלַיִם בְּנוּיוֹת עַל גַּבֵּי הַסֶּלַע וְתַחְתֵּיהֶן חָלוּל מִפְּנֵי קֶבֶר הַתְּהוֹם. וּמְבִיאִין הָיוּ נָשִׁים עֻבָּרוֹת וְיוֹלְדוֹת שָׁם וּמְגַדְּלוֹת שָׁם אֶת בְּנֵיהֶם. וּכְשֶׁיִּרְצוּ לְהַזּוֹת עַל הַכֹּהֵן הַשּׂוֹרֵף מְבִיאִין שְׁוָרִים מִפְּנֵי שֶׁכְּרֵסֵיהֶן נְפוּחוֹת וּמַנִּיחִים עַל גַּבֵּיהֶן דְּלָתוֹת וְיוֹשְׁבִין הַתִּינוֹקוֹת עַל גַּבֵּי הַדְּלָתוֹת כְּדֵי שֶׁיִּהְיֶה הָאֹהֶל מַבְדִּיל בֵּינָם לְבֵין הָאָרֶץ מִפְּנֵי קֶבֶר הַתְּהוֹם. וְכוֹסוֹת שֶׁל אֶבֶן בְּיָדָם וְהוֹלְכִין לַשִּׁילוֹחַ. הִגִּיעוּ לַשִּׁילוֹחַ יוֹרְדִין שָׁם וּמְמַלְּאִין שֶׁאֵין לָחוּשׁ שָׁם מִפְּנֵי קֶבֶר הַתְּהוֹם שֶׁאֵין דֶּרֶךְ בְּנֵי אָדָם לִקְבֹּר בַּנְּהָרוֹת. וְעוֹלִין וְיוֹשְׁבִין עַל גַּבֵּי הַדְּלָתוֹת וְהוֹלְכִין עַד שֶׁמַּגִּיעִין לְהַר הַבַּיִת. הִגִּיעוּ לְהַר הַבַּיִת יוֹרְדִין וּמְהַלְּכִין עַל רַגְלֵיהֶן מִפְּנֵי שֶׁכָּל הַר הַבַּיִת וְהָעֲזָרוֹת תַּחְתֵּיהֶן הָיָה חָלוּל מִפְּנֵי קֶבֶר הַתְּהוֹם. וּמְהַלְּכִין עַד פֶּתַח הָעֲזָרָה. וּבְפֶתַח הָעֲזָרָה הָיָה קָלָל שֶׁל אֵפֶר נוֹטְלִין הָאֵפֶר וְנוֹתְנִין בַּמַּיִם שֶׁבַּכּוֹסוֹת וּמַזִּין עַל הַכֹּהֵן הַשּׂוֹרֵף. וּמַטְבִּילִין הָיוּ הַתִּינוֹקוֹת שֶׁמְּמַלְּאִין וּמְקַדְּשִׁין וּמַזִּין עַל הַשּׂוֹרֵף אַף עַל פִּי שֶׁהֵן טְהוֹרִין מִטֻּמְאַת הַמֵּת שֶׁמָּא נִטְמְאוּ בְּטֻמְאָה אַחֶרֶת:
כסף משנה
7.
When the ashes of the red heifer are sprinkled upon him during the days of his isolation, the sprinkling should be performed by a man who never contracted the ritual impurity stemming from a human corpse. The rationale is that the person sprinkling the ashes must be pure. If one would say: "Let so-and-so, a person who had contracted impurity, but then had the ashes of the red heifer sprinkled upon him, sprinkle the ashes on the priest who will burn the red heifer," that suggestion is not followed. The rationale is that it is possible that the person who sprinkled the ashes upon so-and-so was not pure from the impurity associated with a corpse. Similarly, the utensils that are used to be filled and consecrated to sprinkle on the priest who burns the red heifer were all stone utensils that are not susceptible to ritual impurity. All of these practices are extra stringencies enacted with regard to the red heifer.
How is it possible to find a person who has never contracted the impurity associated with a human corpse? There were courtyards in Jerusalem built on slabs of stone and the space under them was hollow lest there be a grave in the depths of the earth. Pregnant women were brought there; they would give birth there, and raise their sons there. When they wanted to sprinkle ashes on the priest who would burn the red heifer, they would bring oxen - because they have ample bellies - and place doors on their backs and have the children sit on the boards so that there would be an ohel intervening between them and the earth lest they contract impurity from a grave in the depths of the earth. They would have cups of stone in their hands and would go to the Shiloach spring. When they reached the Shiloach, the children would descend and fill the cups. We do not suspect that they will contract impurity from a grave in the depths of the earth at the spring, because it is not ordinary practice to bury the dead in streams.
They would ascend and sit on the doors and proceed upward until they reach the Temple Mount. When they reached the Temple Mount, they would descend and proceed on their feet, because the entire area of the Temple Mount and its courtyards was built over a hollow cavity, lest there be a grave in the depths of the earth.
They would proceed to the entrance to the Temple Courtyard. At the entrance to the Temple Courtyard, there was a pitcher of ashes. They would take the ashes and place them on the water in the cups and sprinkle them on the priest who burns the heifer.
The children who would fill the water, would consecrate it with the ashes and sprinkle it on the priest who burns the heifer must immerse in a mikveh. Even though they are pure with regard to the impurity associated with a human corpse, it is possible that they contracted other forms of impurity.

הלכה ח
תִּינוֹק שֶׁטָּבַל לְמַלְּאוֹת וּלְהַזּוֹת לֹא יְמַלֵּא בְּכֵלָיו תִּינוֹק אַחֵר אַף עַל פִּי שֶׁטָּבַל. וְתִינוֹק שֶׁטָּבַל לְהַזּוֹת עַל כֹּהֵן זֶה אֵינוֹ מַזֶּה עַל כֹּהֵן אַחֵר עַד שֶׁיִּטְבּל לְשֵׁם מַעֲשֶׂה זֶה הַכֹּהֵן. וְכֵן כֵּלִים שֶׁטִּהֲרוּם לְחַטָּאת זוֹ וּבְנֵי אָדָם שֶׁטִּהֲרוּם לְחַטָּאת זוֹ לֹא יִתְעַסֵּק בָּהֶם בְּפָרָה אַחֶרֶת עַד שֶׁיִּטְבְּלוּ לִשְׁמָהּ. וְכָל הַדְּבָרִים הָאֵלּוּ מַעֲלוֹת יְתֵרוֹת בְּפָרָה:
כסף משנה
8.
When a child immersed himself in a mikveh in order to fill pitchers with water and sprinkle it, another child should not fill those containers with water even though he immersed himself.
When a child immersed himself to sprinkle the water of the ashes on one priest, he may not sprinkle the water on another priest until he immerses again for the sake of purifying that priest. Similarly, when utensils or people were purified for the sake of offering one red heifer, they should not become involved in the offering of another red heifer until they immerse themselves for its sake. All of these are extra stringencies required for the offering of the red heifer.

טהרה הלכות פרה אדומה פרק ב
Taharah Para Aduma Chapter 2