קובעת לה וסת עד שתקבענה שלש פעמים ואין מטהרת מן הוסת עד שתעקר ממנה שלש פעמים ושור המועד דתנן אין השור נעשה מועד עד שיעידו בו שלשה פעמים:
establish a set pattern of menstrual bleeding for herself, so that it can be assumed that she will start bleeding at a particular time, until she has established it three times. Similarly, she is not purified from her set pattern until it is uprooted from her three times, i.e., until she did not experience menstrual bleeding at the expected time according to her pattern on three occasions. And the case of a forewarned ox is as we learned in a mishna (Bava Kamma 23b): An ox does not become forewarned until witnesses testify that it has gored three times. Consequently, in the cases of set patterns and a forewarned ox, a legal presumption is created only after three occurrences, in accordance with the opinion of Rabban Shimon ben Gamliel.
ת"ר ניסת לראשון ולא היו לה בנים לשני ולא היו לה בנים לשלישי לא תנשא אלא למי שיש לו בנים נישאת למי שאין לו בנים תצא בלא כתובה
The Sages taught: If a woman was married to her first husband and she did not have children, and then she was married to her second husband and she did not have children, she may not get married to a third husband unless it is to one who already has children and has fulfilled the mitzva to be fruitful and multiply, as it is presumed that she is unable to have children. If she got married to one who does not have children and he had been unaware of her presumptive status, she is divorced without receiving payment for her marriage contract, as he married her erroneously.
איבעיא להו נישאת לשלישי ולא היו לה בנים מהו דליתבעוה הנך קמאי מי מצו אמרי לה איגלאי מילתא דאת הוא דגרמת או דלמא מצית אמרה להו השתא הוא דכחשי מסתברא מצית אמרה להו השתא הוא דכחשי
A dilemma was raised before the Sages: If she was married to a third husband and she did not have children for ten years, what is the halakha with regard to whether those first husbands can demand the return of the money they paid for her marriage contracts? Can they say to her: It has been revealed retroactively that it was you who caused our inability to have children, and therefore we entered our marriages erroneously, or perhaps she can say to them: It is now that I am older that I have become weak, but in my youth I could have had children with a different husband. The Sages answer: It is reasonable that she can say to them: It is now that I have become weak.
איבעיא להו נישאת לרביעי והיו לה בנים מהו דתיתבעיה לשלישי אמרינן לה שתיקותיך יפה מדיבוריך דמצי אמר לה אנא אדעתא דהכי לא גרשתיך
Another dilemma was raised before the Sages: If she was married to a fourth husband and she had children with him, what is the halakha with regard to whether she can demand the payment of her marriage contract from her third husband by claiming that it is now evident that she was capable of having children? The Gemara answers: We say to her: Your silence is preferable to your speech, i.e., you are better off not making this claim, as he can say to her: I did not divorce you with this understanding, and now that I know you are capable of having children, I regret divorcing you. This would invalidate her divorce and, consequently, her marriage to her fourth husband, and would render her child a mamzer.
מתקיף לה רב פפא אי איהי שתקא אנן מי שתקינן נמצא גט בטל ובניה ממזרין אלא אמרינן השתא הוא דברייתא:
Rav Pappa strongly objects to this: If she was silent do we remain silent? If there is room for concern that the divorce might be invalid, the concern exists regardless of her claim, and therefore the bill of divorce should be found invalid and her children from her fourth husband should be rendered mamzerin. Rather, we say that it is now that she has become healthy. In other words, she was previously incapable of bearing children, but she has since recovered from that disability.
הוא אמר מינה והיא אמרה מיניה אמר רבי אמי דברים שבינו לבינה נאמנת וטעמא מאי היא קיימא לה ביורה כחץ הוא לא קים ליה ביורה כחץ
§ The Gemara addresses a related case. If he said that the cause for their failure to have children is from her, i.e., it is she who is infertile, and she said it is from him, Rabbi Ami said: With regard to such matters between him and her, she is believed. The Gemara inquires: What is the reason for this ruling? She is certain whether his semen shoots like an arrow, whereas he is not certain whether his semen shoots like an arrow.
אמר איהו איזיל אינסיב איתתא ואיבדוק נפשאי אמר רבי אמי אף בזו יוציא ויתן כתובה שאני אומר כל הנושא אשה על אשתו יוציא ויתן כתובה רבא אמר נושא אדם כמה נשים על אשתו והוא דאית ליה למיזיינינהי
If he says: I will go and marry a different woman and examine myself to see if I am indeed the cause, Rabbi Ami said: Even in this case he must divorce his first wife and give her the payment for her marriage contract, as I say that whoever marries a woman in addition to his first wife must divorce his first wife and give her the payment for her marriage contract. Conversely, Rava said that a man may marry several women in addition to his first wife, and there is nothing wrong with this practice as long as he has enough to support them all.