Yevamot — Daf 94a

דסניא ליה אמר להו רב ששת תניתוה אמרו לה מת בעליך ואח"כ מת בנך ונשאת ואח"כ אמרו לה חילוף היו הדברים תצא והולד ראשון ואחרון ממזר

היכי דמי אילימא תרי ותרי מאי חזית דסמכת אהני סמוך אהני ועוד ממזר ספק ממזר הוא וכ"ת לא דק הא מדקתני סיפא הראשון ממזר והאחרון אינו ממזר ש"מ דדוקא קתני

אלא לאו חד וטעמא דאתו בי תרי אכחשוה הא לאו הכי מהימן לעולם תרי ותרי וכדאמר רב אחא בר מניומי בעדי הזמה

הכא נמי בעדי הזמה

א"ל רב מרדכי לרב אשי ואמרי ליה רב אחא לרב אשי ת"ש אין האשה נאמנת לומר מת יבמי שאנשא ולא מתה אחותי שאכנס לביתה היא ניהי דלא מהימנא הא עד אחד מהימן

וליטעמיך אימא סיפא אין האיש נאמן לומר מת אחי שאייבם את אשתו ולא מתה אשתי שאשא את אחותה הוא ניהו דלא מהימן הא עד אחד מהימן בשלמא גבי אשה משום עיגונא אקילו בה רבנן אלא גבי איש מאי איכא למימר

אלא כי איצטריך לר"ע איצטריך סד"א הואיל וא"ר עקיבא יש ממזר מחייבי לאוין אימא חיישא אקלקולא דזרעא ודייקא קמ"ל (דאקלקולא דידה חיישא אקלקולא דזרעא לא חיישא)

רבא אמר עד אחד נאמן ביבמה מק"ו לאיסור כרת התרת לאיסור לאו לא כל שכן א"ל ההוא מרבנן לרבא היא עצמה תוכיח דלאיסור כרת התרת לאיסור לאו לא התרת

ואלא איהי מ"ט לא מהימנא דכיון דזימנין דסניא ליה לא דייקא ומינסבא עד אחד נמי דכיון דזמנין דסניא ליה לא דייקא ומינסבא:

זה מדרש דרש רבי אלעזר בן מתיא וכו': אמר רב יהודה אמר רב הוה ליה לר' אלעזר למדרש ביה מרגניתא ודרש ביה חספא

מאי מרגניתא דתניא (ויקרא כא, ז) ואשה גרושה מאישה אפילו לא נתגרשה אלא מאישה פסולה לכהונה והיינו ריח הגט דפוסל בכהונה:

מתני׳ מי שהלכה אשתו למדה"י באו ואמרו לו מתה אשתך ונשא את אחותה ואח"כ באת אשתו מותרת לחזור

hate her brother-in-law?  — R. Shesheth answered them: You have learned it, IF A WOMAN.. WAS TOLD, YOUR HUSBAND DIED AND YOUR SON DIED AFTERWARDS', AND SHE MARRIED AGAIN, AND LATER SHE WAS TOLD, 'IT WAS OTHERWISE', SHE MUST DEPART; AND ANY CHILD BORN BEFORE OR AFTER IS A BASTARD.  Now, how is this to be understood? If it be suggested [that there were] two witnesses against two,  what reason do you see [it may be asked] for relying on the latter? Rely rather on the former! Furthermore, [how could the child be described as a] BASTARD, [when he is only] an uncertain bastard! And should you reply that he  was not exact in his expression. Surely [it may be pointed out] since in the final clause he  stated, ANY CHILD BORN BEFORE [THE DEATH OF HER FIRST HUSBAND] IS A BASTARD, BUT ONE BORN AFTER IT IS NO BASTARD,  it may be inferred that he was exact in his expressions! Consequently  [it must be concluded that the first report was that of] one witness, and that the reason [why he is not believed is] because two witnesses came and contradicted his evidence, but had this not been the case  he would have been believed!  [No]. In fact [it may be retorted, there may have been] two witnesses against two, and [this is the explanation]:  As As R. Aha b. Manyumi stated, 'Where the witnesses have proved an alibi',  so here also [It is a case where the second pair of] witnesses have proved an alibi. Said R. Mordecai to R. Ashi, — others Say. R. Aha said to R. Ashi: Come and hear: A woman is not believed if she says. 'My brother-in-law is dead, and so I may marry again', or, 'My sister is dead, and so I may enter  her house'.  Only she is not believed but one witness is believed!  According to your argument, however, [it may be retorted] read the final clause: A man is not believed when he says.'My brother is dead, and so I may contract the levirate marriage with his wife', or, 'My own wife is dead, and so I may marry her sister' — 10 Is it only he who is not believed, but one witness is believed? In the case of a woman  one can well understand that in order to prevent her perpetual desertion the Rabbis have relaxed the law in her favour.  What, however, can be said in the case of a man! [This statement]  then [it must be explained] was required in accordance with the view of R. Akiba.  It might have been assumed that, since R. Akiba stated that the offspring of a union between those who are subject to the penalty of negative commandments is a bastard, she  may be presumed to be desirous of avoiding injury  and to institute, therefore, careful enquiries.  hence we were taught  [that she is not to be believed]. Raba said:  That one witness is believed in the case of a sister-in-law  [may be inferred] a minori ad majus: If you have permitted [a woman to marry again]  in face of a prohibition involving kareth  how much more so in face of a mere prohibitory law.  Said one of the Rabbis to Raba: Her own case proves [the contrary]: In face of a prohibition involving kareth  you have permitted her [to marry again]  while in face of a mere prohibitory law  you have not permitted her!  The fact, however, is this:  Why is she not believed?  Because, as she may sometimes hate the levir, she might marry a stranger without first instituting careful enquiries;  so also in the case of one witness, since she may sometimes hate the levir, she might marry [a stranger] without first instituting the necessary enquiries. THIS DID R. ELEAZAR B. MATHIA DERIVE BY MEANS OF THE FOLLOWING EXPOSITION etc. Said Rab Judah in the name of Rab:  R. Eleazar could have produced  a pearl and produced but a potsherd. What is meant by 'pearl'? — That which was taught: Neither [shall they take] a woman put away from her husband.  even if she was divorced from her husband alone  she  is disqualified from marrying a priest.  And it is this [that was meant by] the 'scent of the divorce'  which disqualifies a woman from marrying a priest. MISHNAH. IF A MAN'S WIFE HAD GONE TO A COUNTRY BEYOND THE SEA AND HE WAS TOLD,  YOUR WIFE IS DEAD', AND, AFTER HE MARRIED HER SISTER, HIS WIFE CAME BACK, [THE LATTER] IS PERMITTED TO RETURN