פּירוש אויף ויקרא 15:25

‎ימים רבים [AND IF A WOMAN HAVE AN ISSUE OF HER BLOOD] MANY DAYS — at least three days (since the plural ימים suggests at least two days, the word רבים, “more", must imply at least three days) (cf. Sifra, Metzora Parashat Zavim, Section 5 9),

בלא עת נדתה, after the days of her menstruation have passed, as explained in Niddah 73 A woman is not described as being a zavah so that she would have to bring an offering after being healed unless the seven days during which she was a menstruant or expected to be a menstruant have passed. If after that period during the next 11 days she sees the symptoms of a zavah for three consecutive days she will require to count seven consecutive days during which she is free of these symptoms in order to be able to become ritually pure again. On the eighth day she is ready to offer her two bird offerings, one as a sin offering the other as a burnt offering.

ימים רבים, “many days.” Our sages (Sifra Zavim section 5, items 8-9) define the word רבים here as “three.” They reason as follows: had the Torah spoken only of ימים, “days,” I would have assumed that what is meant is two days. Why would I have concluded that the word ימים refers to only two and not many? Rabbi Akiva said that whenever a word lends itself to two possible interpretations, one involving more than the other, I choose the minimum meaning compatible with that word; in this instance the minimum of ימים is “two.”
Rabbi Nechemyah said: Does then the text of the Torah mean to confuse us? Surely it is meant to enlighten us! If you were to say that the word ימים without the addition רבים could have meant either ten, a hundred, or two hundred, etc., the choices would be unlimited and confusing. Therefore by understanding the word ימים as meaning the minimum, i.e. “two,” the Torah opened the way for us to understand its meaning.
Rabbi Mona said: the word ימים without further detail means “two.” In the event I would have thought that it means many days this would be superfluous as the Torah already wrote the word רבים, “many.” This indicates that the total number of days the Torah had in mind were relatively few. Seeing that such a minimum of a few days is two, it stands to reason that the word רבים increases this number by a further minimum, i.e. one day more, i.e. a total of three days.

בלא עת נדתה OUT OF THE TIME OF HER SEPARATION — i. e. at least three days immediately after the seven normal days of her separation have expired.