Halacha

הלכה א
כָּל הָעוֹסְקִין בַּפָּרָה מִתְּחִלָּה וְעַד סוֹף מְטַמְּאִין בְּגָדִים כָּל זְמַן עֲשִׂיָּתָן שֶׁנֶּאֱמַר בְּשׁוֹחֵט וּמַשְׁלִיךְ עֵץ אֶרֶז (ויקרא טו יג) "וְכִבֶּס בְּגָדָיו וְרָחַץ בְּשָׂרוֹ" וְנֶאֱמַר בְּשׂוֹרֵף (במדבר יט ח) "וְהַשֹּׂרֵף אֹתָהּ יְכַבֵּס בְּגָדָיו" וְנֶאֱמַר (במדבר יט י) "וְכִבֶּס הָאֹסֵף אֶת אֵפֶר הַפָּרָה" מְלַמֵּד שֶׁכָּל הָעוֹסְקִין בָּהּ מִתְּחִלָּה וְעַד סוֹף מְטַמְּאִים בְּגָדִים וּטְעוּנִין טְבִילָה וְהַעֲרֵב שֶׁמֶשׁ דִּין תּוֹרָה. אֲבָל הַמְשַׁמְּרָהּ בִּשְׁעַת עֲשִׂיָּתָהּ מְטַמֵּא בְּגָדִים מִדִּבְרֵיהֶם גְּזֵרָה שֶׁמָּא יָזִיז בָּהּ אֵיבָר:
כסף משנה
1.
All of those involved in offering the red heifer from the beginning to the end become impure and impart impurity to their garments as long as they are involved in its being offered. This concept is derived as follows: With regard to the one who slaughters the heifer and one who casts the cedar wood into its belly, Numbers 19:7 states: "The priest shall launder his clothes and wash his flesh." And with regard to the one who burns it, ibid.:8 states: "The one who burns it shall launder his clothes," and ibid.:10 states: "The one who gathers the ashes of the heifer shall launder...."
These verses teach that all those involved in offering it from the beginning until the end impart impurity to their clothes, must immerse themselves, and wait for nightfall to regain purity according to Scriptural Law. One who guards the heifer at the time it is being offered imparts impurity to his garments according to Rabbinic Law. This is a decree lest he move one of its limbs.

הלכה ב
כָּל מָקוֹם שֶׁנֶּאֱמַר בַּתּוֹרָה בְּטֻמְאוֹת יְכַבֵּס בְּגָדָיו לֹא בָּא לְלַמְּדֵנוּ שֶׁהַבְּגָדִים שֶׁעָלָיו בִּלְבַד הֵם טְמֵאִים. אֶלָּא לְלַמֵּד שֶׁכָּל בֶּגֶד אוֹ כְּלִי שֶׁיִּגַּע בּוֹ הַטָּמֵא הַזֶּה בִּשְׁעַת חִבּוּרוֹ בִּמְטַמְּאָיו הֲרֵי הֵן טְמֵאִים. אֲבָל אַחַר שֶׁיִּפְרשׁ מִמְּטַמְּאָיו אֵינוֹ מְטַמֵּא בְּגָדִים. כֵּיצַד. הַנּוֹשֵׂא אֶת הַנְּבֵלָה אֶחָד בֶּגֶד שֶׁעָלָיו אוֹ כְּלִי שֶׁיִּגַּע בּוֹ כָּל זְמַן שֶׁהוּא נוֹשְׂאָהּ הֲרֵי הֵן טְמֵאִין וַהֲרֵי הֵן רִאשׁוֹן לְטֻמְאָה. וְכֵן זֶה הַנּוֹשֵׂא הֲרֵי הוּא רִאשׁוֹן. פֵּרַשׁ מִמְּטַמְּאָיו וְהִשְׁלִיךְ אֶת הַנְּבֵלָה הֲרֵי הוּא רִאשׁוֹן כְּמוֹת שֶׁהָיָה. וְאִם יִגַּע בִּכְלִי אוֹ בֶּגֶד אֵינוֹ מְטַמֵּא אוֹתוֹ שֶׁאֵין וְלַד טֻמְאָה מְטַמֵּא כֵּלִים כְּמוֹ שֶׁבֵּאַרְנוּ בִּתְחִלַּת סֵפֶר זֶה. וְכֵן כָּל כַּיּוֹצֵא בִּנְבֵלָה. וְכֵן כָּל הָעוֹסְקִין בַּפָּרָה אִם נָגַע בְּבֶגֶד אוֹ בִּכְלִי בִּשְׁעַת שְׁחִיטָה אוֹ בִּשְׁעַת שְׂרֵפָה הֲרֵי הֵן טְמֵאִין. אֲבָל אַחַר שֶׁיִּפְרשׁ מִמַּעֲשֶׂיהָ אַף עַל פִּי שֶׁעֲדַיִן לֹא טָבַל אִם נָגַע בִּכְלִי אֵינוֹ מְטַמְּאוֹ מִפְּנֵי שֶׁהוּא וְלַד הַטֻּמְאָה. וְהַפָּרָה עַצְמָהּ אֵינָהּ מְטַמְּאָה לֹא אָדָם וְלֹא כֵּלִים שֶׁנָּגְעוּ בּוֹ. אֶלָּא הַמִּתְעַסֵּק בָּהּ בִּלְבַד הוּא הַטָּמֵא וְטָעוּן טְבִילָה וּמְטַמֵּא בְּגָדִים כָּל זְמַן שֶׁעוֹסֵק בָּהּ:
כסף משנה
2.
Whenever the Torah states with regard to impurity: "One shall launder his clothes," it does not come merely to teach that the clothes on a person are impure. Instead, it teaches that every garment or implement that this impure person will touch while he is still in contact with the object that imparted impurity to him becomes impure. After he separates himself from the object that imparted impurity to him, he does not impart impurity to his garments or to other objects.
What is implied? A person who carries an animal carcass imparts impurity to the clothes he is wearing and to any implement he touches as long as he is carrying it. They are considered as a first degree derivative of impurity. Similarly, the one who carries the animal carcass is considered as impure to the first degree. If he ceased contact with the object that imparted ritual impurity, casting away the animal carcass, he remains impure to the first degree as before. If, however, he touches an implement or a garment, he does not impart impurity to it, for a derivative of ritual impurity does not impart impurity to implements, as we explained in the beginning of this text. Similar laws apply to all types of impurity analogous to that imparted by an animal carcass.
Similarly, with regard to all those involved in offering the red heifer: If they touch a garment or an implement at the time they are slaughtering or burning the heifer, it becomes impure. After such an individual ceased the tasks involved with it, however, even though he has not yet immersed, he does not impart impurity to an implement that he touches, because he is merely a derivative of impurity.
The red heifer itself does not impart impurity to a person or to implements that touch it. It is only those involved in its offering who become impure, must immerse themselves, and impart impurity to their garments, as long as they are involved in its offering.

הלכה ג
בַּמֶּה דְּבָרִים אֲמוּרִים בִּזְמַן שֶׁנִּשְׂרֶפֶת כְּמִצְוָתָהּ. אֲבָל אִם נִפְסְלָה הַמִּתְעַסֵּק בָּהּ טָהוֹר. אֵרַע פִּסּוּל בִּשְׁחִיטָתָהּ אֵינָהּ מְטַמְּאָה בְּגָדִים. אֵרַע פִּסּוּל בְּהַזָּיָתָהּ כָּל הָעוֹסֵק בָּהּ לִפְנֵי פִּסּוּלָהּ מְטַמֵּא בְּגָדִים. לְאַחַר פִּסּוּלָהּ אֵינוֹ מְטַמֵּא בְּגָדִים:
כסף משנה
3.
When does the above apply? When the red heifer was burnt as prescribed. If, however, it was disqualified, those involved in offering it are pure. If a disqualifying factor occurred during its slaughter, it does not cause a person's garments to become impure. If a disqualifying factor occurs during the sprinkling of its blood, those who were involved with its offering before it was disqualified impart impurity to their garments. Those involved after its disqualification do not impart impurity to their garments.

הלכה ד
הִשְׁלִים לִכְנֹס אֶת אֶפְרָהּ הַמִּתְעַסֵּק בָּהּ אַחַר כֵּן בְּחִלּוּק הֶעָפָר אוֹ בְּהַצְנָעָתוֹ וְכֵן הַנּוֹגֵעַ בּוֹ טָהוֹר. וְלֹא הַפָּרָה בִּלְבַד אֶלָּא כָּל הַחַטָּאוֹת הַנִּשְׂרָפוֹת מִן הַפָּרִים וּמִן הַשְּׂעִירִים הַשּׂוֹרְפָם מְטַמֵּא בְּגָדִים בִּשְׁעַת שְׂרֵפָתוֹ עַד שֶׁיֵּעָשׂוּ אֵפֶר. שֶׁהֲרֵי הוּא אוֹמֵר בְּפַר וְשָׂעִיר שֶׁל יוֹם הַכִּפּוּרִים (ויקרא טז כח) "וְהַשֹּׂרֵף אֹתָם יְכַבֵּס" מִפִּי הַשְּׁמוּעָה לָמְדוּ שֶׁזֶּה בִּנְיַן אָב לְכָל הַנִּשְׂרָפִים שֶׁיְּהוּ מְטַמְּאִין בְּגָדִים עַד שֶׁיֵּעָשׂוּ אֵפֶר. בַּמֶּה דְּבָרִים אֲמוּרִים בְּשֶׁלֹּא אֵרַע לָהֶן פִּסּוּל וְנִשְׂרְפוּ כְּמִצְוָתָן בְּבֵית הַדֶּשֶׁן. אֲבָל אִם נִפְסְלוּ בָּעֲזָרָה נִשְׂרָפִין שָׁם כִּפְסוּלֵי הַמֻּקְדָּשִׁין וְשׂוֹרְפָן טָהוֹר. וְכֵן הַמִּתְעַסֵּק בָּהֶן מִשֶּׁיֵּעָשׂוּ אֵפֶר אֵינוֹ מְטַמֵּא בְּגָדִים. וְאֵי זֶהוּ שׂוֹרֵף זֶה הַמַּסִּיעַ בִּשְׂרֵפָה כְּגוֹן הַמְהַפֵּךְ בַּבָּשָׂר וְהַמַּשְׁלִיךְ עֵצִים וְהַמְהַפֵּךְ בָּאֵשׁ וְהַחוֹתֶה גֶּחָלִים כְּדֵי שֶׁתִּבְעַר הָאֵשׁ וְכַיּוֹצֵא בָּהֶן. אֲבָל הַמַּצִּית הָאוּר וְהַמְסַדֵּר אֶת הַמַּעֲרָכָה טָהוֹר. כָּךְ לָמְדוּ מִפִּי הַשְּׁמוּעָה שֶׁהַנּוֹשֵׂא פָּרִים וּשְׂעִירִים הַנִּשְׂרָפִין לְהוֹצִיאָן לְבֵית הַדֶּשֶׁן לְשָׂרְפָן טָמֵא וּמְטַמֵּא בְּגָדִים דִּין תּוֹרָה כָּל זְמַן שֶׁהוּא עוֹסֵק בְּהוֹלָכָתָן וְטָעוּן טְבִילָה וְהַעֲרֵב שֶׁמֶשׁ. כְּמוֹ הַמְשַׁלֵּחַ אֶת הַשָּׂעִיר לַעֲזָאזֵל שֶׁהוּא מְטַמֵּא כָּל בֶּגֶד וְכָל כְּלִי שֶׁיִּגַּע בּוֹ בְּכֵלִים שֶׁעָלָיו כָּל זְמַן שֶׁמִּתְעַסֵּק בִּשְׁלוּחוֹ שֶׁנֶּאֱמַר (ויקרא טז כו) "וְהַמְשַׁלֵּחַ אֶת הַשָּׂעִיר לַעֲזָאזֵל יְכַבֵּס בְּגָדָיו":
כסף משנה
4.
When the collection of its ashes was completed, anyone who is involved with it - i.e., with the division of its ashes or with setting them aside for safekeeping - or who touches it, is pure.
These principles do not apply to the red heifer alone, but also to all the sin-offerings of bulls and goats that are burnt. One who burns them imparts impurity to his garments while he is burning them until they are reduced to ashes. For behold, with regard to the bull and the goat burned on Yom Kippur, Leviticus 16:25 states: "The one who burns them shall launder his garments." According to the Oral Tradition, it was taught that this is a general rule applying to all those who burn sacrificial offerings, teaching that they impart impurity to their garments until the offerings are reduced to ashes.
When does the above apply? When no disqualifying factor occurred and they were burned in the ashheap as prescribed. If, however, they were disqualified in the Temple Courtyard, they are burned there like disqualified offerings and the one who burns them is ritually pure. Similarly, one who is involved with these offerings after they have been reduced to ashes does not impart impurity to his garments.
Who is considered as "one who burns" it? Anyone who helps in burning it, for example, one who turns over the meat, one who places wood upon it, one who fans the fire, one who stirs the coals so that the fire will burn, and the like. In contrast, one who kindles the flame and one who builds the arrangement are pure.
According to the Oral Tradition, it was taught that one who carries the bulls and the goats that are burnt to transport them to the ashheap to burn them is ritually impure and imparts impurity to his garments according to Scriptural Law as long as he is involved in transporting them. To regain purity, he is required to immerse himself in a mikveh and wait until nightfall like the one who sends the goat to Azazel. The latter imparts impurity to all the garments and all the implements that he touches that are on him throughout the time he is involved in sending the goat to its destination, as ibid.:26 states: "The one who sends the goat to Azazel shall launder his garments."

הלכה ה
מֵאֵימָתַי מְטַמְּאִין בְּגָדִים הַנּוֹשְׂאִין פָּרִים וּשְׂעִירִים הַנִּשְׂרָפִים. מִשֶּׁיֵּצְאוּ בָּהֶן חוּץ לְחוֹמַת הָעֲזָרָה. נְשָׂאוּם בְּמוֹטוֹת וְיָצְאוּ מִקְצָת הַנּוֹשְׂאִים חוּץ לְחוֹמַת הָעֲזָרָה וְהָאַחֲרוֹנִים לֹא יָצְאוּ. אֵלּוּ שֶׁיָּצְאוּ מְטַמְּאִין בְּגָדִים וְאֵלּוּ שֶׁעֲדַיִן לֹא יָצְאוּ אֵינָן מְטַמְּאִין בְּגָדִים עַד שֶׁיֵּצְאוּ. יָצְאוּ וְחָזְרוּ לָעֲזָרָה הַנּוֹשֵׂא אוֹתָן בָּעֲזָרָה טָהוֹר עַד שֶׁיֵּצֵא בָּהֶן. הָיָה עוֹמֵד חוּץ לָעֲזָרָה וּמוֹשֵׁךְ אוֹתָם מִשָּׁם מֵאַחַר שֶׁחָזְרוּ הוֹאִיל וּכְבָר יָצְאוּ לַחוּץ וַהֲרֵי זֶה הַמּוֹשְׁכָם בַּחוּץ הֲרֵי הוּא סְפֵק טָמֵא:
כסף משנה
5.
From when do those who carry the bulls and goats that are burnt impart impurity to their garments? When they take them out of the Temple Courtyard. If they carried them with poles and some of those carrying them left the walls of the Temple Courtyard and others did not depart, those that departed impart impurity to their garments. Those who did not yet depart do not impart impurity to their garments until they depart.
If they depart and then return to the Temple Courtyard and transfer the carcasses to others, the others who carry them in the Temple Courtyard are pure until they take them out.
If a person was standing outside the Courtyard and was pulling the poles on which the carcasses were hanging from the Courtyard after they were returned there, he is considered as being impure of doubtful status, since the sacrificial animals had already been taken outside and the one pulling them was standing outside.

הלכה ו
וּמֵאֵימָתַי מְטַמֵּא בְּגָדִים הַמְשַׁלֵּחַ אֶת הַשָּׂעִיר. מִשֶּׁיֵּצֵא חוּץ לְחוֹמַת יְרוּשָׁלַיִם עַד שְׁעַת דְּחִיָּתוֹ לַעֲזָאזֵל. אֲבָל אַחַר שֶׁדָּחָהוּ אִם נָגַע בְּכֵלִים וּבִבְגָדִים טְהוֹרִים:
כסף משנה
6.
When does the person who sends the goat to Azazel impart impurity to his garments? From the time he departs Jerusalem until he pushes the goat off the cliff to Azazel. After he pushes it off the cliff, if he touches implements or garments, they are pure.

הלכה ז
הַנּוֹגֵעַ בְּפָרִים וּבִשְׂעִירִין הַנִּשְׂרָפִין עַצְמָן אֲפִלּוּ אַחַר שֶׁיָּצְאוּ בֵּין אָדָם בֵּין כֵּלִים בֵּין אֳכָלִין בֵּין מַשְׁקִין הַכּל טָהוֹר. וְכֵן אִם נָגְעוּ בַּשָּׂעִיר הַמִּשְׁתַּלֵּחַ עַצְמוֹ בִּזְמַן הוֹלָכָתוֹ טְהוֹרִין. שֶׁאֵין אֵלּוּ מְטַמְּאִין אֶלָּא לַמִּתְעַסֵּק בָּהֶן בִּלְבַד שֶׁנֶּאֱמַר (במדבר יט ח) "וְהַשֹּׂרֵף אֹתָהּ יְכַבֵּס בְּגָדָיו" אֲבָל הַנּוֹגֵעַ טָהוֹר:
כסף משנה
7.
When an entity - whether a person, an implement, food, or liquid - touches the bodies of the bulls and the goats that are burnt, even after they have been taken out of the Temple Courtyard, everything is pure. Similarly, if they would touch the goat sent to Azazel itself while it is being carried there, they would be pure. For these sacrificial animals impart impurity only to one who is involved with carrying them, as indicated by Leviticus 16:28: "The one who burns them shall launder his garments." One who touches, by contrast, is pure.

טהרה הלכות פרה אדומה פרק ה
Taharah Para Aduma Chapter 5