Sotah, Chapter Six, Mishnah Four
The last mishnah of this chapter deals with a case where there is contradictory testimony with regard to whether or not she committed adultery (was defiled). We should remember that there has already been a process of warning before these witnesses come and testify.
1) If one witness says that she was defiled and another witness says that she was not defiled;
a) Or if a woman says [of her] that she was defiled and another woman says that she was not defiled, she drinks.
2) If one witness says that she was defiled and two say that she was not defiled, she drinks.
3) If two say that she was defiled and one says that she did not, she does not drink.
Section one: The testimony of the first witness is contradicted by that of the second witness; each witnesss testimony nullifies that of the other. Since there is no testimony that she was defiled but there was evidence that she was warned and secluded, she drinks the water. The same is true if both witnesses are women. Although women are generally not allowed to testify, they are allowed to testify in this case. However, since they contradict each other, their testimony is nullified.
Section two: In this case, after one witness testifies that she was defiled, two witnesses testify that she was not defiled. One might have thought that this would have been sufficient not only to nullify the first testimony, but to totally prove her innocence. However, it is still possible that she was defiled before the witnesses saw that she was not (they had completed their adulterous act before the witnesses saw them). Since she was after all secluded with the man whom her husband suspects, she must drink the sotah waters in order to establish her innocence.
Section three: Since two witnesses say that she was defiled, a single witness who says that she was not defiled cannot nullify their testimony. Hence, it is established that she has committed adultery and therefore she does not drink the water. Rather she becomes prohibited to her husband and loses her ketubah.