Gittin 36B

ותקינו רבנן דתשמט, זכר לשביעית; ראה הלל שנמנעו העם מלהלוות זה את זה, עמד והתקין פרוסבול.

And the rabbis instituted that despite this, the Sabbatical Year still will abrogate debt in the present, in remembrance of the Torah-mandated Sabbatical Year. Hillel saw that the people of the nation refrained from lending to each other so he arose and instituted the prosbol. According to this explanation, the ordinance of Hillel did not conflict with a Torah law; rather, he added an ordinance to counter the effect of a rabbinic law.

ומי איכא מידי דמדאורייתא לא משמטא שביעית, ותקינו רבנן דתשמט?!

According to this explanation, the rabbis instituted that even in the present the Sabbatical Year would bring a cancellation of debt, despite the fact that by Torah law the debt still stands. The Talmud asks: But is there anything like this, where by Torah law the Sabbatical Year does not cancel the debt, and the rabbis instituted that it will cancel? It is as though the rabbis are instructing the debtors to steal from their creditors, as by Torah law they still owe the money.

אמר אביי: שב ואל תעשה הוא. רבא אמר: הפקר בית דין ⁠– הפקר. דאמר רבי יצחק: מנין שהפקר בית דין ⁠– הפקר? שנאמר: ״וכל אשר לא יבוא לשלשת הימים כעצת השרים והזקנים, יחרם כל רכושו והוא יבדל מקהל הגולה״.

Abaye says: This is not actual theft; it is an instruction to sit passively and not do anything. The rabbis have the authority to instruct one to passively violate a Torah law, so long as no action is taken. Rava says: The rabbis are able to institute this ordinance because property declared ownerless by the court is ownerless. As R' Yitzḥak says: From where is it derived that property declared ownerless by the court is ownerless? As it is stated: “And whoever did not come within 3 days according to the counsel of the princes and the Elders, all of his property should be forfeited, and he should be separated from the congregation of the captivity” (Ezra 10:8).