Mishnayos Niddah Perek 9 Mishnah 5

In a case of three women who were sleeping in one bed that was located adjacent to a wall, and blood was discovered beneath the middle woman, all of them are ritually impure. If the blood was discovered beneath the woman on the inside, closest to the wall, the two innermost women are ritually impure and the woman on the outside is ritually pure. If the blood was discovered beneath the woman on the outside, farthest from the wall, the two outermost women are ritually impure and the woman on the inside is ritually pure. When is that the ruling? It is when they passed into their positions on the bed via the foot of the bed; but if they passed into their positions on the bed via the side of the bed, over the place where the blood was discovered, all of them are ritually impure. If immediately after the blood was discovered, one of them examined herself and she was found to be ritually pure, she is pure and the other two are impure. If two of them examined themselves and found that they were ritually pure, they are pure and the third is impure. If all three of them examined themselves and found that they were ritually pure, all of them are ritually impure, as the blood must have originated from one of them. To what case is this matter comparable? It is similar to the case of a ritually impure pile of stones with an olive-bulk of a corpse beneath it, where this pile was intermingled with two ritually pure piles, and they examined one of them and found it pure. That pile is pure and the other two are impure. If they examined two of them and found them ritually pure, they are ritually pure and the third is impure. If they examined all three of them and found them ritually pure, all of them are impure; this is the statement of Rabbi Meir, as Rabbi Meir would say: With regard to any item that has the presumptive status of ritual impurity, it forever remains in its state of ritual impurity, even if one examined the relevant area or item and the source of impurity was not found, until it becomes known to you where the ritual impurity is. The assumption is that the impurity was not found because the examination was not conducted properly. And the Rabbis say: One continues searching the relevant area until he reaches bedrock or virgin soil, beneath which there is certainly no ritual impurity. If no ritual impurity is found at that stage, presumably an animal dragged the olive-bulk of the corpse from beneath the pile, and the pile of rocks is pure.

שָׁלשׁ נָשִׁים שֶׁהָיוּ יְשֵׁנוֹת בְּמִטָּה אַחַת וְנִמְצָא דָם תַּחַת הָאֶמְצָעִית, כֻּלָּן טְמֵאוֹת. תַּחַת הַפְּנִימִית, שְׁתַּיִם הַפְּנִימִיּוֹת טְמֵאוֹת וְהַחִיצוֹנָה טְהוֹרָה. תַּחַת הַחִיצוֹנָה, שְׁתַּיִם הַחִיצוֹנוֹת טְמֵאוֹת וְהַפְּנִימִית טְהוֹרָה. אָמַר רַבִּי יְהוּדָה, אֵימָתַי, בִּזְמַן שֶׁעָבְרוּ דֶרֶךְ מַרְגְּלוֹת הַמִּטָּה. אֲבָל אִם עָבְרוּ שְׁלָשְׁתָּן דֶּרֶךְ עָלֶיהָ, כֻּלָּן טְמֵאוֹת. בָּדְקָה אַחַת מֵהֶן וְנִמְצֵאת טְהוֹרָה, הִיא טְהוֹרָה וּשְׁתַּיִם טְמֵאוֹת. בָּדְקוּ שְׁתַּיִם וּמָצְאוּ טְהוֹרוֹת, הֵן טְהוֹרוֹת וְהַשְּׁלִישִׁית טְמֵאָה. שְׁלָשְׁתָּן וּמָצְאוּ טְהוֹרוֹת, כֻּלָּן טְמֵאוֹת. לְמַה הַדָּבָר דּוֹמֶה, לְגַל טָמֵא שֶׁנִּתְעָרֵב בֵּין שְׁנֵי גַלִּים טְהוֹרִים, וּבָדְקוּ אַחַד מֵהֶן וּמָצְאוּ טָהוֹר, הוּא טָהוֹר וּשְׁנַיִם טְמֵאִין. שְׁנַיִם וּמָצְאוּ טְהוֹרִים, הֵם טְהוֹרִים וְהַשְּׁלִישִׁי טָמֵא. שְׁלָשְׁתָּן וּמָצְאוּ טְהוֹרִים, כֻּלָּן טְמֵאִים, דִּבְרֵי רַבִּי מֵאִיר, שֶׁהָיָה רַבִּי מֵאִיר אוֹמֵר, כָּל דָּבָר שֶׁהוּא בְחֶזְקַת טֻמְאָה, לְעוֹלָם הוּא בְטֻמְאָתוֹ, עַד שֶׁיִּוָּדַע לְךָ, טֻמְאָה הֵיכָן הִיא. וַחֲכָמִים אוֹמְרִים, בּוֹדֵק עַד שֶׁמַּגִּיעַ לְסֶלַע אוֹ לִבְתוּלָה: