The Mishna ruled that if there were two groups of witnesses and each group denied knowing testimony, both groups are liable. The Gemara raises a difficulty with this case, arguing that the first group should not be liable since another group of witnesses can still testify. Ravina resolves this difficulty by limiting the Mishna's ruling to a specific case: where the second group of witnesses are related to each other (as their wives are sisters) and both wives are about to die when the first group takes their oath denying knowledge of the testimony.
The Mishna lists various cases where witnesses are asked to testify about multiple things. In some cases, they are only liable one sacrifice and in others multiple sacrifices.
An oath of testimony only applies in monetary cases. A question is asked: Does this also include cases involving fines (kenas)? Before answering this question, the Gemara limits the question to the rabbis' position in their debate with Rabbi Elazar son of Rabbi Shimon. Rabbi Elazar rules that if someone admits owing a fine, they are exempt, but if witnesses come forward even after the confession, they are obligated to pay the fine. Therefore, an oath of testimony would clearly apply here, since the witnesses would definitively obligate the defendant. However, the rabbis hold that witnesses can only obligate the defendant if they testify before a confession. Therefore, the question arises whether an oath of testimony would apply here, since it's possible the witnesses are not causing a loss to the claimant—the defendant could simply confess and be exempt. This question is further limited by assuming the rabbis also hold by the position of the rabbis on a different issue: that davar hagorem l'mamon (something that can possibly lead to a monetary obligation) is not considered a monetary obligation. Rabbi Elazar ben Rabbi Shimon disagrees and holds that such potential obligations are considered monetary obligations which would obligate the witnesses a sacrifice if they do not testify. After establishing these parameters for the question, the Gemara examines various cases from our Mishna and other sources to attempt an answer. However, neither source provides a conclusive resolution.
From where do they derive that an oath of testimony is only for monetary cases? Four different rabbis each bring different proofs.