Yevamot

that [once a woman was married she] is not taken away because of a mere rumour; and so here also [the woman married] is not to be taken away because of a rumour. MISHNAH. IF ALL THESE  HAD WIVES  WHO [SUBSEQUENTLY] DIED, [THE OTHER WOMEN]  ARE PERMITTED TO MARRY THEM.  IF THEY  WERE MARRIED TO OTHERS  AND WERE [SUBSEQUENTLY] DIVORCED,  OR WIDOWED, THEY MAY BE MARRIED TO THESE.  THESE  ARE ALSO PERMITTED TO THEIR  SONS OR BROTHERS. GEMARA. Only if they  died  but not if they were divorced.  Said R. Hillel to R. Ashi: Surely, it was taught: Even if they were divorced! — This is no difficulty: The one  refers to the case where they led  a quarrelsome life;  the other,  where they  had no quarrels.  If you prefer I might say that the one as well as the other [refers to the case] where there were no quarrels, and yet there is no difficulty: The former  is a case where the husband had led on [to the divorce];  in the latter,  she led on to the divorce. IF THEY WERE MARRIED etc. It was now assumed that death  has reference to the case of death,  and divorce  to that of divorce.  Must it then be said that our Mishnah  is in disagreement the delivery of the letter of divorce by the messenger, or the evidence of the man who testified to their husbands' deaths. with the view of Rabbi? For had it been in agreement with Rabbi, [a third marriage would not have been allowed], for he said that two occurrences constitute a hazakah.  — No;  death  [has reference] to divorce,  and divorce  to death. THESE ARE ALSO PERMITTED TO THEIR SONS OR BROTHERS. Wherein is this different from the following where it was taught:  A man who is suspected of intercourse with a woman is forbidden to marry her mother, her daughter and her sister.  -It is the usual thing for women to pay frequent visits to other women;  it is not usual, however, for men to pay frequent visits to other men.  Or [this] also:  Women who do not cause one another to be forbidden by their cohabitation  do not particularly mind one another;  men, however, who do cause one another to be forbidden by their cohabitation  do mind one another.  If so,  [the same law  should] also [apply to] one's father!  -The meaning is, 'There is no need',  [thus]: There is no need [to state that the law  is applicable to] one's father before whom a son is shy;  but [in the case of] one's son  before whom a father  is not shy it might have been assumed [that this law was] not [to be applied], hence we were informed [that the same law was applicable to a son also]. MISHNAH. [IN THE CASE OF] FOUR BROTHERS, TWO OF WHOM WERE MARRIED TO TWO SISTERS, IF THOSE WHO WERE MARRIED TO THE SISTERS DIED, BEHOLD. THESE  MUST PERFORM HALIZAH BUT MAY NOT BE TAKEN IN LEVIRATE MARRIAGE [BY THE BROTHERS].  IF THEY HAD ALREADY  MARRIED THEM, THEY MUST DISMISS THEM. R. ELIEZER SAID: BETH SHAMMAI HOLD THAT THEY MAY RETAIN THEM, AND BETH HILLEL HOLD THAT THEY MUST DISMISS THEM. IF ONE OF THE SISTERS  WAS FORBIDDEN TO ONE [OF THE BROTHERS] UNDER THE PROHIBITION OF INCEST,  HE IS FORBIDDEN TO MARRY HER BUT MAY MARRY HER SISTER,  WHILE TO THE SECOND BROTHER BOTH ARE FORBIDDEN. [IF ONE SISTER]  WAS FORBIDDEN BY VIRTUE OF A COMMANDMENT  OR BY VIRTUE OF HOLINESS  SHE MUST PERFORM THE HALIZAH BUT MAY NOT BE TAKEN IN LEVIRATE MARRIAGE. IF ONE OF THE SISTERS  WAS FORBIDDEN TO ONE BROTHER UNDER THE LAW OF INCEST AND THE OTHER SISTER WAS FORBIDDEN TO THE OTHER UNDER THE LAW OF INCEST, SHE WHO IS FORBIDDEN TO THE ONE IS PERMITTED TO THE OTHER AND SHE WHO IS FORBIDDEN TO THE OTHER IS PERMITTED TO THE FIRST. THIS IS THE CASE CONCERNING WHICH IT HAS BEEN SAID: WHEN HER SISTER IS HER SISTER-IN-LAW  SHE MAY EITHER PERFORM HALIZAH OR BE TAKEN IN LEVIRATE MARRIAGE. GEMARA. This then  implies that a levirate bond exists;  for if no levirate bond exists, observe this point: These widows come from two different houses,  let one brother take in levirate marriage the one and the other brother the other!  — As a matter of fact it may still be assumed that no levirate bond exists  [but the levirate marriage is nevertheless forbidden] because he  is of the opinion that it is forbidden to annul the precept of levirate marriage, it being possible that while one of the brothers married [one of the widowed sisters] the other brother would die,  and the precept of levirate marriage would be annulled.  If so,  [the same applies to] three [brothers] also!  — This may be regarded as the case of 'There is no need etc.';  thus: There is no need to state three,  since the precept of levirate marriage would inevitably have to be annulled;  but [in the case of] four  [it might have been assumed that] one need not take precautions against [possible] death,  hence we were informed [that even in such a case levirate marriage is forbidden].  If so,