Gittin, Chapter 4, Mishnah 8. This Mishnah continues the topic of the previous Mishnah: cases in which a man who divorces his wife may no longer take her back.
The View of Rabbi Yehudah:
If a man divorces his wife because she appears to be barren and unable to bear children - Rabbi Yehudah says "lo yachazir" - he may not take her back. At the time of the divorce he is told explicitly: be aware that you will not be able to take her back. Once he was warned of this from the outset, he can no longer claim later on, when it turns out that she has borne children, "Had I known that you were able to bear children I would never have divorced you," since he was already told at the time the get was given that there is no going back afterwards.
The Relationship to the Previous Mishnah:
At first glance this seems to contradict Rabbi Yehudah's words in the previous Mishnah: there, in the case of a man who divorces his wife because of a vow, Rabbi Yehudah was not concerned about a possible complication, whereas here he is concerned. The answer is that there the reasoning was different, and a distinction must be drawn between two types of vows:
A vow that requires a sage to annul it: where he caused her to have to come before a beis din - here Rabbi Yehudah held like Rabbi Elazar, that a man does not want his wife to be degraded by having to go to beis din. Therefore the husband cannot fall back on the claim that he would never have divorced her.
A vow that does not require a sage to annul it: where the husband's own annulment suffices - here he held like Rabbi Meir, that everyone knows that it is in the husband's power to annul the vow, and he is expected to know this. Consequently he cannot say, "Had I known, I would not have divorced her."
Not so in our case: here Rabbi Yehudah is concerned about a complication, because of the possibility that she was never barren at all.
The View of the Sages:
And the Sages say "yachazir" - he may take her back. The Gemara explains that this position follows the view of Rabbi Meir, who holds that any condition that is not formulated like the condition of the children of Gad and the children of Reuven is not a valid condition. The children of Gad and the children of Reuven made a double condition with Moshe Rabbeinu: if they would go and fight in Eretz Yisrael they would receive the land, and if they would not go they would not receive it - they stated the condition in both directions. In our case the husband did not state his condition in both directions, and therefore he has no ability to come and challenge the validity of the get. For this reason there is no concern about a complication, and he may take his wife back after having divorced her.
According to this understanding, we will have to say that the case in the previous Mishnah involved a double condition.
"Nissa'as le'acher vehayu lah banim heimenu":
She married another man and bore him children - so it has become clear that she was not barren - "vehi tova'as kesubasah" - and she claims her kesubah. She comes and argues: you divorced me and did not give me my kesubah, because you claimed that this was a mistaken marriage, a mistaken transaction, since I am unable to bear children. And now it has become clear that I am able to bear children, so the kesubah is due to me.
To this Rabbi Yehudah says: we tell her "shesikusayich yafah lich midibburayich" - your silence serves you better than your speech. For if she insists on her claim to the kesubah, the husband will come and say that the get he gave her was never valid, and it will emerge that her second marriage is void and her children are mamzerim. Therefore we say to her: be silent and do not make an issue of this, for you have no interest in the husband coming and claiming that he never had any reason to divorce you.
In summary: In this Mishnah, Rabbi Yehudah and the Sages disagree about a man who divorces his wife because of barrenness. According to Rabbi Yehudah he may not take her back, since he is warned at the time of the divorce that there is no going back afterwards, and out of concern for the complication that perhaps she was never barren at all. According to the Sages, following Rabbi Meir's view regarding the law of a double condition, the husband cannot challenge the get, and therefore he may take her back. We also learned that if she married another man and bore him children and she claims her kesubah, Rabbi Yehudah tells her, "Your silence serves you better than your speech," so as not to raise any challenge to the validity of the get and to the status of her children.