Mishnah Niddah 7

¹The blood of a menstruant and the flesh of a corpse convey uncleanness when wet and when dry. But the discharge [of a zav], and the phlegm [of a zav] and the spittle [of a zav], a dead sheretz, a nevelah and semen convey uncleanness when wet but not when dry. If they can be soaked and then revert to their original condition they convey uncleanness when wet and when dry. And how long must they be soaked? In lukewarm water for a period of twenty four hours. Rabbi Yose says: If the flesh of a corpse is dry, and it cannot be soaked and brought back to its original condition, it is clean. ²If a dead sheretz was found in an alley it causes uncleanness retrospectively to such time as one can say, "I examined this alley and there was no sheretz in it," or to such time as it was last swept. So also a bloodstain found on a garment causes uncleanness retrospectively to such time as one can say, "I examined this shirt and there was no stain on it" or to such time as it was last washed. And it conveys uncleanness whether it is wet or dry. Rabbi Shimon says: if it is dry it causes uncleanness retrospectively, but if it is wet it causes uncleanness only to a time when it could still have been wet. ³All bloodstains that come from Rekem are clean. Rabbi Judah declares them unclean, because the people who live there are proselytes though misguided. Those that come from non-Jews are clean. Those that come from Israelites or from Samaritans: Rabbi Meir declares them unclean, But the sages declare them clean because they are not suspected in regard to their stains. ⁴All bloodstains, wherever they are found are clean except those that are found in rooms or in a house for unclean women. A house for unclean Samaritan women conveys uncleanness by overshadowing because they bury miscarriages there. Rabbi Judah says: they did not bury them but threw them away and the wild beasts dragged them off. ⁵They are believed when they say, "we buried miscarriages there," or "we did not bury them." They are believed when they say concerning a beast whether it had given birth to a firstling or had not given birth to one. They are believed when giving information on the marking of graves. But they are not believed either in regard to overhanging branches, or protruding stones or a bet ha-peras. This is the general rule: in any matter in which they are under suspicion they are not believed.