Niddah 53: Women Finding a Blood Stain

We have already learned that becoming ritually impure as a niddah is learned from Vayikra (15:19), where it says, "And if a woman has an issue, and her issue in her flesh is blood, she will be in her ritual impurity seven days; and anyone who touches her will be ritually impure until the evening".  

The rabbis understand this passage as referring to 

• a flow of blood
• the sensation of the flow of blood

If a woman finds a ketem, stain, on her clothing, the Torah does not say that she is a niddah.  However, the Sages ruled that she is a niddah based on their rabbinic ruling alone.  The Gemara say that Rabbi Yehuda HaNasi taught: if a woman sees a bloodstain and then sees a discharge of blood, she is permitted to assume that the blood has flowed within twenty-four hours. Rabbi Shimon ben Elazar ruled that it must be during the same day.  Thus the status of niddah does not extend back to when the clothing was washed but only since the moment it was found, as long as these events were within a twenty-four hour period.  Rabbi Elazar limits this to one day.   

Rabbi Betzalel Ranschberg teaches that there is no clear ruling on this matter.  However, it is irrelevant because Rabbi Zeira ruled successfully that women must wait seven "clean" days after seeing even one spot of blood.