The early sages (Tanaaim) ruled that a man who has been married for ten years and has not had children may divorce his wife and marry another so he may fulfill the commandment to be fruitful and multiply. The divorced wife may marry again; she is not forbidden to wed in the fear that should will not become pregnant. If in her second marriage she still does not manage to bear children within ten years and her husband divorces her for this, she may not wed a third time. This stand, the scholars argue, coincides with the opinion of Rabbi Judah the Nasi, who ruled that if the first son in a family is circumcised and dies and the second son is circumcised and dies, the third son is not circumcised lest he, too, die. In his opinion, two incidents are enough from which to generalize and forecast the future. According to Rabban Shimon son of Gamliel three cases are required before the future can be forecast. This is learned from the testimony of the scholar Rabbi Chiyya son of Abba about four sisters. One of them gave birth to a son who was circumcised and died, and then the same happened to another sister, and to another. When the fourth sister gave birth to a boy she asked Rabban Shimon son of Gamliel whether to circumcise her son or not and she was told it was forbidden due to fear her son would die. The scholars asked: Is it possible that had the third sister asked Rabban Shimon son of Gamliel would also have forbidden her to circumcise her son? Answer: If that were so, what about Rabbi Chiyya’s testimony? You are forced to admit that he testified that only after three similar cases do we fear that there will be an equal danger the fourth time. The scholars then asked: Perhaps Rabbi Chiyya’s testimony was intended to teach that we do not require a single woman to have given birth to three sons, that even sisters who give birth, women of the same family, can be added together to make up the incidents. Incidentally, the scholar Rava learned that if a woman has an epileptic sister, one should not marry the woman. Let us return to clarifying our question — what was the opinion of Rabban Shimon son of Gamliel about the number of repeated incidents require to create fear about the next incident? Were two incidents enough, or were three required? Answer: An additional incident is related, in which a woman gave birth to two sons who were circumcised and died. When a third son was born she asked Rabban Gamliel and was given permission to circumcise him. This shows that three repeated incidents are required before we fear for another repeat. Based on this determination the scholar Abaye married Huma, though she had already been married twice. Though her two previous husbands had died, Abaye did not fear he, too, would die, because he relied upon the opinion of Rabban Shimon son of Gamliel. After he married Huma he, too, died. The scholar Rava wondered how Abaye could marry with such a threat over his head. There were, after all, sages who thought that if the same thing happened twice one should fear a further repeat. He also wondered how Abaye compared an incident involving circumcision to one involving marrying a widow. The scholars answered him: Since the sons died after circumcision and the husbands died, they are comparable. The students asked why one should hesitate to marry a woman who had two husbands who died. The fear of death following circumcision is obvious, for there is a family connection involving blood types or genetics, but a woman whose husbands have died — what is there to fear? Answer: One of the scholars answered that the woman apparently has some sexually transmitted disease which causes her husbands’ deaths, “the source is the cause.” A different scholar, Rav Ashi, gave a different explanation, that the woman has bad luck which causes her husband to die. The scholars asked: What is the difference between the two answers? Answer: A case in which the husband dies before having sexual intercourse with her. According to the one who says that the woman has a sexually transmitted disease, there is no reason to fear, for they did not have sexual relations, so he could not have caught a fatal illness from her. According to the one who says that she has bad luck, even if they were married but did not yet have sexual relations he must fear marrying her, lest her bad luck kill him, too.
(Babylonian Talmud, Tractate Yevamot 64b)