Niddah, Chapter 1, Mishnah 4. This chapter is built around a single question: when a woman discovers blood, does her tumah begin only at that moment, or does it reach backward in time? The halachah speaks of two possibilities. One is mei'eis le'eis, retroactive tumah covering the previous twenty four hours, which means that taharos she handled during that stretch are treated as temei'im. The other is dayah sha'atah, that her moment suffices: she is temeiah from when she saw and not a minute earlier. Until now the mishnah has associated dayah sha'atah with a woman whose vesses is fixed, whose period arrives at a predictable time each month. Our mishnah adds a group of women who receive this same leniency even though their timing is not regular at all.
"Rebbi Eliezer omer, arba nashim dayan sha'atan." Rebbi Eliezer teaches that there are four women whose moment is enough for them. These are women without a vesses kavua, women who do not become nidos at a set time month after month, and yet no retroactive tumah is imposed on them. Their tumah runs from the moment of seeing and forward, mikan ulehaba.
Who are the four?
- Besulah, a virgin.
- Me'uberes, a woman who is pregnant.
- Meinekas, a woman who is nursing.
- Zekeinah, an older woman, one who has already passed the years of seeing.
Each of these four is in a stage of life in which we do not expect the usual pattern, and therefore Rebbi Eliezer holds that there is no basis for reaching backward into the previous day and declaring her earlier contacts temei'im.
Rebbi Yehoshua's dissent
Rebbi Yehoshua objects: "Amar Rebbi Yehoshua, ani lo shamati ela bivesulah." The tradition he received covered a single case, that of the besulah. To his mind she is the one woman on the list who escapes the backward reach of tumah, while the me'uberes, the meinekas and the zekeinah are all governed by the standard din and are rendered temei'os for the preceding twenty four hours as well.
The final word
The mishnah refuses to leave the machlokes hanging. Its concluding words are a psak: "Aval halachah keRebbi Eliezer." We rule like Rebbi Eliezer. Every one of the four women he listed is judged by dayan sha'atan, so that her tumah begins where the seeing begins and moves only forward, leaving the hours before it entirely untouched.