Ketubot 215:1

שוקל לו את שקלו ופורע את חובו ומחזיר לו אבידתו ובמקום שנוטלין שכר תפול הנאה להקדש

[his neighbor] may pay his shekel, pay off his debts, and return a lost article to him. Where payment is taken for this, the benefit should become sacred property.

בשלמא שוקל לו את שקלו מצוה קעביד דתנן תורמין על האבוד ועל הגבוי ועל העתיד לגבות

It makes sense that he may “pay for him his shekel” [because by this payment] he merely performs a mitzvah, for it was taught: One may withdraw [from the funds of the Temple treasury] on the account of that which was lost, collected or about to be collected;

ומחזיר לו אבידתו נמי מצוה קעביד אלא פורע לו את חובו הא קמשתרשי ליה

And one who returns to him a lost object is also performing a mitzvah. But “repay his debt”—is this not providing him with a direct benefit?

אמר רב אושעיא הא מני חנן היא דאמר איבד את מעותיו

Oshaya replied: Who is this [that rules thus?] It is Hanan, who said, “he has lost his money.”

ורבא אמר אפי' תימא רבנן הכא במאי עסקינן שלוה על מנת שלא לפרוע

Rava said: You can say that the ruling agrees even with the rabbis. What are we dealing with here? With one who borrowed money on the condition that he does not repay it [except when he wants to].

בשלמא רבא לא אמר כרב אושעיא דמוקים לה כרבנן אלא רב אושעיא מ"ט לא אמר כרבא אמר לך רב אושעיא נהי דהנאה לית ליה

It makes sense that Rava does not say as did R. Oshaia, since [he wishes] the ruling to agree even with the opinion of the rabbis. But why does R. Oshaia not resolve the problem like Rava? R. Oshaia could answer you: Granted that he does not have actual benefit,