Ketubot 27B

מה לי לשקר. או דלמא לא אמרינן?

Why would I lie in so ineffectual a manner, and deem her credible? Had she wanted to lie, she could have claimed that she hid, which is a more effective claim. Or perhaps we do not say that principle.

ומאי שנא מההוא מעשה, דההוא גברא דאגר ליה חמרא לחבריה, אמר ליה: לא תיזיל באורחא דנהר פקוד דאיכא מיא, זיל באורחא דנרש דליכא מיא, ואזל איהו באורחא דנהר פקוד ומית חמרא.

The Talmud asks: And in what way is this different from that incident where a certain man who rented a donkey to his colleague said to the renter: Do not go on the path of the Pekod River, where there is water, and the donkey is likely to drown. Go on the path of Neresh, where there is no water. And he went on the path along the Pekod River and the donkey died.

אתא לקמיה דרבא, אמר ליה: אין, באורחא דנהר פקוד אזלי, מיהו לא הוו מיא. אמר רבא: ״מה לי לשקר״. אי בעי, אמר ליה: באורחא דנרש אזלי. ואמר ליה אביי: ״מה לי לשקר״ במקום עדים לא אמרינן.

The renter came before Rava and said to him: Yes, I went on the path along the Pekod River; however, there was no water there. The donkey’s death was caused by other factors. Rava said: His claim is accepted based on the principle: Why would I lie. If he wanted to lie, he could have said to him, I went on the path of Neresh. And Abaye said to Rava: We do not say the principle: Why would I lie, in a situation where there are witnesses. This principle, which is a form of miggo, is effective only when his claim does not contradict established facts. In this case, since it is known to all that there is water on the path along the Pekod River, his claim is not accepted. Similarly, as it is an established fact that the women taken captive were certainly raped, her claim is not accepted even though it is based on a miggo.