Shevuot 33A

הא קיימא שניה!

But the second set of witnesses still stands available to testify, so what loss did the first set cause the plaintiff when they denied knowledge of the matter?

אמר רבינא: הכא במאי עסקינן ⁠– כגון שהיתה שניה בשעת כפירת ראשונה קרובין בנשותיהן, ונשותיהן גוססות; מהו דתימא: רוב גוססים למיתה, קא משמע לן: השתא מיהא לא שכיב.

Ravina said: What are we dealing with here? We are dealing with a case where the two witnesses in the second set were relatives through their wives at the time of the denial of the first set of witnesses. The two witnesses in the second set were married to two sisters, and brothers-in-law are unfit to serve as witnesses together. Therefore, the claim of the plaintiff is entirely dependent upon the testimony of the first set of witnesses. And the sisters who were wives of the witnesses in the second set were moribund. Lest you say that since, presumably, the majority of individuals who are moribund will actually die very soon, and therefore these two witnesses are fit to testify together, therefore, the tanna teaches us that since now in any event, the wives had not yet died, their husbands remain unfit to testify together.

מתני׳ ״משביע אני עליכם, אם לא תבואו ותעידוני שיש לי ביד פלוני פקדון ותשומת יד וגזל ואבידה״; ״שבועה שאין אנו יודעין לך עדות״⁠ – אין חייבין אלא אחת.

Mishnah: In a case where the plaintiff said to the witnesses: I administer an oath to you concerning your refusal to testify if you do not come and testify on my behalf that I have in the possession of so-and-so a deposit, and an outstanding loan, and a stolen item, and a lost item, and they lied in reply: On our oath we do not know any testimony on your behalf, they are liable for taking only one false oath of testimony.