Yevamot 118A

אשה אומרת: ״מת״, ואשה אומרת: ״לא מת״⁠ — הרי זו לא תנשא.

or one woman says: He died, and another woman says: He did not die, this woman may not marry.

גמ׳ טעמא דאמרה ״לא מת״, הא אישתיקא ⁠— תנשא? הא אין צרה מעידה לחברתה!

Talmud: The Mishnah taught that if one rival wife says their husband died, while the second maintains that he did not die, the one who says he did not die may not remarry. The Talmud infers: The reason is that the second rival wife said explicitly: He did not die, from which it may be inferred that if she was silent and said nothing, she is permitted to marry based on the testimony of the first. However, this conclusion is problematic, as there is a principle that one rival wife may not testify on behalf of another, and if so, how can she rely on the testimony of her rival wife?

״לא מת״ איצטריכא ליה, סלקא דעתך אמינא: הא מיית, והא דקאמרה ״לא מת״⁠ — לקלקולה לצרה היא דקמיכוונא, ו״תמות נפשה עם פלשתים״ קאמרה, קמשמע לן.

The Talmud answers that this inference is incorrect, as it was necessary for the Mishnah to state: He did not die, as it might enter your mind to say that this man did in fact die, and with regard to that which she says: He did not die, she intends to ruin her rival wife. And as for herself she says: Let her die with the Philistines. This is a paraphrase of the verse: “Let me die with the Philistines” (Judges 16:30), which is a shorthand expression for one’s desire to hurt his enemies even if he suffers the same fate himself. In this case it means that she is prepared to testify falsely that their husband did not die, so as to ruin her rival wife. Therefore the Mishnah teaches us that this is not the case, and she is not permitted to marry based on the testimony of her rival wife.