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(א) כָּל הַטְּמֵאִין בֵּין אָדָם בֵּין כֵּלִים בֵּין שֶׁנִּטְמְאוּ טֻמְאָה חֲמוּרָה שֶׁל תּוֹרָה בֵּין שֶׁנִּטְמְאוּ בְּטֻמְאָה שֶׁל דִּבְרֵיהֶן אֵין לָהֶן טָהֳרָה אֶלָּא בִּטְבִילָה בְּמַיִם הַנִּקְוִין בְּקַרְקַע:
(ב) כָּל מָקוֹם שֶׁנֶּאֱמַר בַּתּוֹרָה רְחִיצַת בָּשָׂר וְכִבּוּס בְּגָדִים מִן הַטֻּמְאָה אֵינוֹ אֶלָּא טְבִילַת כָּל הַגּוּף בְּמִקְוֶה. וְזֶה שֶׁנֶּאֱמַר בְּזָב (ויקרא טו יא) "וְיָדָיו לֹא שָׁטַף בַּמָּיִם" כְּלוֹמַר שֶׁיִּטְבֹּל כָּל גּוּפוֹ. וְהוּא הַדִּין לִשְׁאָר הַטְּמֵאִין שֶׁאִם טָבַל כֻּלּוֹ חוּץ מֵרֹאשׁ אֶצְבַּע הַקְּטַנָּה עֲדַיִן הוּא בְּטֻמְאָתוֹ. וְכָל הַדְּבָרִים הָאֵלֶּה אַף עַל פִּי שֶׁהֵן מִפִּי הַשְּׁמוּעָה הֲרֵי נֶאֱמַר (ויקרא יא לב) "בַּמַּיִם יוּבָא וְטָמֵא עַד הָעֶרֶב וְטָהֵר" בִּנְיַן אָב לְכָל הַטְּמֵאִים שֶׁיָּבוֹאוּ בַּמַּיִם:
(1) Whatever is defiled, whether human beings or utensils, whether rendered unclean by some grave uncleanness on biblical grounds or by some uncleanness on rabbinic grounds, can become clean only by immersion in water that is gathered on the ground [not within a receptacle].
§ The mishna further taught that the halakhot of ritual purity have something to support them. The Gemara again asks: But ritual purity is written explicitly in the Torah. The Gemara answers: The observation that the halakhot of ritual purity merely have something to support them is necessary only for the minimum measure of a ritual bath, which is not written explicitly in the Torah. As it is taught in a baraita: “And he shall bathe his flesh in water” (Leviticus 14:9). This means in the water of a ritual bath. And it is stated: “And he shall wash all his flesh in water” (Leviticus 15:16), which indicates that it must contain water in which his whole body can enter. And how much water is this? One cubit by one cubit with a height of three cubits. And the Sages estimated that the measure for ritual bath water is forty se’a.
חֲצִיצִין, דְּאוֹרָיְיתָא נִינְהוּ! דִּכְתִיב: ״וְרָחַץ אֶת כָּל בְּשָׂרוֹ (בַּמַּיִם)״, שֶׁלֹּא יְהֵא דָּבָר חוֹצֵץ בֵּין בְּשָׂרוֹ לַמַּיִם....
Rabbi Ḥiyya bar Ashi said above that Rav said that the laws governing interpositions that invalidate ritual immersion are halakhot transmitted to Moses from Sinai. The Gemara challenges this assertion: These, too, are written in the Torah, as it is written: “And he shall bathe all his flesh in the water” (Leviticus 15:16), and the Sages derived that nothing should intervene between his flesh and the water...