Niddah 57b
נדה נ״ז ב — ד"ה גְּמָ' אָמַר שְׁמוּאֵל
Niddah 57b:5
Chachmei Bavel state that a woman who checked the ground, sat on it, and then found blood is ritually pure because impurity requires sensing an emission, while “in her flesh” also teaches that the blood must be in contact with her flesh rather than in a gestational sac or detached piece.
גְּמָ' אָמַר שְׁמוּאֵל: בָּדְקָה קַרְקַע עוֹלָם, וְיָשְׁבָה עָלֶיהָ, וּמָצְאָה דָּם עָלֶיהָ — טְהוֹרָה, שֶׁנֶּאֱמַר ״בִּבְשָׂרָהּ״ — עַד שֶׁתַּרְגִּישׁ בִּבְשָׂרָהּ. הַאי ״בִּבְשָׂרָהּ״ מִיבְּעֵי לֵיהּ, שֶׁמְּטַמְּאָה בִּפְנִים כְּבַחוּץ! אִם כֵּן, לֵימָא קְרָא ״בְּבָשָׂר״, מַאי ״בִּבְשָׂרָהּ״? שְׁמַע מִינַּהּ: עַד שֶׁתַּרְגִּישׁ בִּבְשָׂרָהּ. וְאַכַּתִּי מִיבְּעֵי לֵיהּ ״בִּבְשָׂרָהּ״, וְלֹא בְּשָׁפִיר וְלֹא בַּחֲתִיכָה! תַּרְתֵּי שְׁמַע מִינַּהּ.
GEMARA: With regard to the cases discussed in the mishna concerning a blood stain found on a woman, Shmuel says: If a woman examined the ground beneath her to see if it was clean from blood and other substances, and she found nothing, and subsequently she sat upon it and then found blood on it, although it might be assumed that this blood came from her, she is ritually pure. The reason is as it is stated: “And her issue in her flesh shall be blood, she shall be in her menstrual state seven days” (Leviticus 15:19). This verse teaches that a woman does not become impure unless she senses, i.e., experiences some type of sensation, in her flesh that she emitted blood from her uterus. Since this woman did not sense an emission of blood, she is pure. The Gemara asks: How can Shmuel interpret the verse in this manner? After all, he requires this term: “In her flesh,” to teach a different halakha, that a woman becomes impure by finding blood inside her body just as by seeing blood outside her body, i.e., provided that the blood is uterine blood, even if it is currently situated inside her vaginal canal, she is impure. The Gemara answers: If so, if it serves to teach only that blood inside is like blood outside, let the verse say: In the flesh. What is the reason that the verse states: “In her flesh”? Conclude from this term that a woman does not become impure unless she senses in her flesh. The Gemara asks: And still, Shmuel requires the term “in her flesh” to teach that she is impure only if the blood touches her flesh, and not through blood found in a gestational sac, nor through blood found in an amorphous piece of tissue that she emitted. The Gemara answers: Conclude two conclusions from this verse, as the plain meaning of the term teaches all these halakhot.