Mishnah Niddah 8

¹If a woman observed a bloodstain on her body: If it was opposite her genital area she is unclean; But if it was not near the genital are she remains clean. If it was on her heel or on the tip of her large toe, she is unclean. On her thigh or on her feet: If on the inner side, she is unclean; If on their outer side, she remains clean. And if on the front and back sides she remains clean. If she observed it on her garment: Below the belt, she is unclean, But if above the belt, she remains clean. If she observed it on the sleeve of her shirt: If it can reach as low as her genital area, she is unclean, But if it cannot, she remains clean. If she takes it off and covers herself with it in the night, she is unclean wherever the stain is found, since it can turn about. And the same law applies to a pallium. ²[A woman] may attribute [a bloodstain] to any [external] cause to which she can possibly attribute it. If [for instance] she had slaughtered a beast, a wild animal or a bird, Or if she was handling bloodstains or if she sat beside those who handled them. Or if she killed a louse, she may attribute the bloodstain to it. How large a stain may be attributed to a louse? Rabbi Hanina ben Antigonus says: one up to the size of a split bean; And even if she did not kill it. She may also attribute it to her son or to her husband. If she herself had a wound that could open again and bleed she may attribute it to it. ³It happened that a woman came in front of Rabbi Akiva and said. She said to him: I have seen a bloodstain. He said to her: Perhaps you had a wound? She said to him: Yes, but it has healed. He said to her: Perhaps it could have opened again and let out some blood." She said to him: Yes. And Rabbi Akiva declared her clean. He saw his disciples looked at each other in astonishment. He said to them: Why do you find this difficult, for the sages did not say this rule in order to be stringent but rather to be lenient, for it is said, "And if a woman have issue, and her issue in her flesh be blood" blood but not a bloodstain. ⁴A testing rag that was placed under a pillow and some blood was found: If it is round it is clean If it is elongated it is unclean, the words of Rabbi Elazar bar Zadok.