Shevuos Daf 31 חג השבועות דַף 31

A Baraisa lists thirteen activities which are prohibited in Beis Din because they violate מדבר שקר תרחק – distance yourself from falsehood, including using false methods to bring about correct rulings. For example, if a teacher tells his student (who knows he would never lie for money), that someone owes him money, but he has only one witness against him, the student cannot stand with the witness, even silently, to give the impression there are two witnesses, thereby causing the defendant to admit his debt. Also, if one is owed a maneh, he may not say, אטעננו במאתים כדי שיודה לי במנה – I will claim two hundred [zuz] from him, so he will admit to owing me a maneh, ויתחייב לי שבועה – and he will become obligated to swear to me that he does not owe a second maneh (as a מודה במקצת), and I will require him to swear about a other claims through the principle of גלגול שבועה.

Also, we derive that if three people are owed money by one borrower, שלא יהא אחד בעל דין ושנים עדים – that one cannot act as the litigant and the other two as witnesses, כדי שיוציאו מנה ויחלוקו – so they can collect the maneh they are jointly owed and divide it between themselves.

In the Mishnah, Rebbe Meir said that one who swears מפי עצמו – with his own mouth (to deny knowing testimony) is liable even if he swore outside of Beis Din. If others were משביע him ("מפי אחרים"), he is only liable if his denial was in Beis Din. The Chochomim hold that regardless of who expressed the shevuah, he is only liable for a denial in Beis Din. The liability for שבועת העדות is only written in a case of מושבע מפי אחרים, about a denial in Beis Din. Swearing מפי עצמו is derived from a shevuah about a פקדון. Rebbe Meir holds: דון מינה ומינה – “derive the law from it and derive the parameters from it.” Just as with פקדון, מושבע מפי עצמו חייב – if an oath is said by [the שומר]’s own mouth, he is liable, the same applies to the shevuah of עדים. And just as with פקדון, the liability applies both inside and outside of Beis Din, the same applies to שבועת העדות when they themselves express the shevuah. The Rabbonon hold: דון מינה ואוקי באתרה – derive the law from it, but establish its parameters according to its own place. Since שבועת העדות was only written about a shevuah in Beis Din, the derived law of swearing מפי עצמו also only applies in Beis Din.

The next Mishnah teaches that שבועת העדות only applies if the litigant first tells them, בואו והעידוני – “Come and testify for me,” but not if they swear on their own (Shmuel adds that even if he was running after them and they swore, they would be exempt). If he was משביע them five times outside of Beis Din, and when they came to Beis Din, they again denied knowing testimony, חייבין על כל אחת ואחת – they are liable for each and every [shevuah]. However, if he was משביע them five times in Beis Din and they denied knowing testimony, they are only liable once. Rebbe Shimon explains: הואיל ואינם יכולין לחזור ולהודות – because they are not able to retract and admit to knowing testimony after having denied it in Beis Din. Once they testify in Beis Din that they have no knowledge of any testimony, we apply the principle of כיון שהגיד שוב אינו חוזר ומגיד – once [a witness] related testimony, he cannot retract and relate contradictory testimony. Since he is no longer able to testify on the litigant’s behalf, he is not liable for denying it a second time.