Ketubot 18A

דסתם יהודה וגליל כשעת חירום דמו.

The Talmud answers: The reason that the tanna cited specifically a case where each is located in a different land is that the standard situation with regard to travel between Judea and the Galilee is tantamount to a crisis period, as war was commonplace, and there was a strip of Samaritan territory between Judea and the Galilee.

וליתני: מודה רבי יהושע באומר לחבירו ״מנה לויתי ממך ופרעתיו לך״, שהוא נאמן! משום דקא בעי למיתני סיפא: אם יש עדים שהוא לוה ממנו, והוא אומר: פרעתיו ⁠— אינו נאמן, והא קיימא לן המלוה את חבירו בעדים ⁠— אינו צריך לפרעו בעדים.

The Talmud asks: And let the tanna teach in the Mishnah: And R' Yehoshua concedes in a case where one says to another: I borrowed 100 dinars from you and repaid the loan to you, that he is deemed credible. The Talmud answers: The tanna chose not to teach that case of the mouth that prohibited is the mouth that permitted due to the fact that the tanna wanted to teach in the latter clause: If there are witnesses that he borrowed money from another, and he says: I repaid the loan, he is not deemed credible. However, the tanna would not be able to distinguish between a case where witnesses testify and a case where there are no witnesses, as don’t we hold that in the case of one who lends money to another in the presence of witnesses, the borrower need not repay the loan in the presence of witnesses? Therefore, even if witnesses testify that he took the loan, his claim that he repaid the loan is accepted.

וליתני: מודה רבי יהושע באומר לחבירו: מנה לאביך בידי, והאכלתיו פרס ⁠— שהוא נאמן!

The Talmud asks: And let the tanna teach in the Mishnah: And R' Yehoshua concedes in a case where one says to another: Your father has 100 dinars in my possession in the form of a loan, but I provided him with repayment of half that amount, that his claim is deemed credible.