Sotah, Chapter 6, Mishnah 2. This mishnah continues to discuss witnesses whose testimony is normally not accepted, and who nevertheless have the power to affect the outcome. Here, however, the testimony does not concern the seclusion, as in the previous mishnah, but rather the defilement itself - that the woman actually had relations while she was secluded.
"Amar ed echad: ani re'isiha shenitmes":
If a single witness testifies "ani re'isiha shenitmes" - that he saw her, during the time she was secluded, having forbidden relations - then "lo haysah shosah" - she does not drink. For the Torah says "and there was no witness against her," which implies that if there is a witness, even a single witness, she does not drink, and she is divorced without her kesubah.
The testimony of a slave and a maidservant:
The mishnah adds that even a slave and even a maidservant - "harei elu ne'emanin" - are believed. Their credibility is not limited to preventing her from drinking the sotah waters; rather, it extends "af lifsolah mikesubasah" - even to disqualifying her from her kesubah, and she remains forbidden to her husband. This is because a warning and a seclusion have already taken place here - a significant sequence of events, in which her husband warned her and she nevertheless secluded herself. Under these circumstances she forfeits her kesubah even on the testimony of a slave or a maidservant who testify that she was defiled.
The five women suspected of hating her:
The mishnah lists five women who have a connection to the sotah. The Gemara in Yevamos explains that although normally the testimony of a single woman suffices to establish that a woman's husband has died and that she may remarry, these five women are presumed - or at least suspected - to hate her because of their relationship to her. Since they are suspected of hating her, there is a concern that they wish to ruin her, and therefore they are not believed to say that her husband died. Our mishnah teaches that nevertheless, in the case before us their testimony carries a certain force.
Her mother-in-law.
Her mother-in-law's daughter.
Her rival wife - married to the same husband.
Her sister-in-law - where they were married to two brothers.
Her husband's daughter - her stepdaughter.
All of these, although they are not believed with regard to testimony that the husband has died, here "harei elu ne'emanos" - they are believed, but only to this extent: to say that she had relations while she was secluded, and therefore she does not drink the sotah waters.
"Velo lifsolah mikesubasah, ela shelo sishteh" - for this consequence they are not believed, since they hate her. The only thing they are believed for is the stringency, that we do not allow her to drink. She remains forbidden to her husband, but she does not lose her kesubah on account of their testimony.
In summary: In this mishnah we learned that testimony about the sotah's defilement is accepted even from a single witness, and even from a slave or a maidservant - both to prevent her from drinking and to disqualify her from her kesubah. But the five women suspected of hating her are believed only halfway: for the stringency, that she does not drink and remains forbidden to her husband, but not to cause her to forfeit her kesubah.