Sotah 32A

והכא במאי עסקינן ⁠— כגון דאתאי אשה מעיקרא.

And with what are we dealing here in the Mishnah? A case where a woman, who is generally disqualified from bearing witness, came initially, and testified that the woman committed adultery, and two witnesses say that she did not.

ותרצה לדרבי נחמיה הכי, רבי נחמיה אומר: כל מקום שהאמינה תורה עד אחד ⁠— הלך אחר רוב דיעות, ועשו שתי נשים באשה אחת כשני אנשים באיש אחד. אבל שתי נשים באיש אחד ⁠— כי פלגא ופלגא דמי.

And according to this interpretation you must amend the statement of R' Neḥemya so that it reads like this: R' Neḥemya says: Wherever the Torah relies on one witness, follow the majority of opinions. And the rabbis established that two women against one woman are like two men against one man. But two women in opposition to one man that is a valid witness, is like half of a pair of witnesses and a half of a pair of witnesses, and the Mishnah did not address that case.

ותרתי בפסולי עדות למה לי? מהו דתימא: כי אזלינן בתר רוב דיעות לחומרא, אבל לקולא לא אזלינן, קא משמע לן.

The Talmud poses a question on these two interpretations of the Mishnah: And why do I need two cases in the Mishnah to teach the halakha that the majority opinion of those disqualified from bearing witness is followed? The Talmud explains: It is necessary, lest you say that when we follow the majority opinion in the case of invalid witnesses, this is to be stringent to force the woman to drink the bitter water, e.g., if one witness said that she committed adultery and two said that she did not, but to be lenient and absolve her from having to drink the water we do not follow the majority opinion, and she would still drink the water even if there is one witness saying that she did not commit adultery, therefore the Mishnah teaches us that there is no difference in this regard, and the majority opinion is followed in any case.