Parashat Re'eh - Halachic Heavy Lifting - Prosbul / Prozbul

Deuteronomy 15

(1) At the end of every seven years you shall make a release. (2) And this is the manner of the release: every creditor shall release that which he lent to his neighbour; he shall not exact it of his neighbour and his brother; because the LORD’S release hath been proclaimed. ... (3) your hand shall release whatever is yours which is with your brother.

(9) Beware that there be not a base thought in thy heart, saying: ‘The seventh year, the year of release, is at hand’; and your eye be evil against your needy brother, and you give him nought; and he cry to the LORD against you, that will be your sin.

Mishnah Gittin 4:3

Witnesses sign on a bill of divorce, due to Tikkun HaOlam. Hillel instituted the pruzbul due to Tikkun HaOlam.

Mishnah Shviit 10:3

Any loan made with a Pruzbul is not cancelled. This is one of the matters that Hillel the elder instituted. When he observed that the nation withheld from lending to each other and were transgressing what is written in the Torah "Beware lest there be in your mind a base thought," he instituted the Pruzbul.

(4) This is the body of the Pruzbul: "I entrust to you, so-and-so and so-and-so, who judge in such-and-such place, that any loan that I have, I may collect it any time that I wish." And the judges affix their signatures below, or the witnesses.

Yerushalmi, Shevi'it 39c

"That debt matters which you have with your brother, your hand shall remit" (Deut 15:3) - and not someone who deposited his contracts at the court. This is the source that indicates that the prozbul is biblical. But is the prozbul Biblical? When Hillel established it, he did so on the basis of biblical law."

Babylonian Talmud, Gittin 36b

Shmuel Said: One cannot write a prozbul other than for the courts of Sura or Nehardea.

Paul Heger, The Pluralist Halachah p. 104n
The Sages, though they used hermeneutic rules, were not bound by a particular systematic method, but rather were guided by certain principles they deemed important.
The concept of hierarchy among halachic rules, allowing one precept to override another, provided to the Sages a far-reaching philosophical foundation on which to base various rules, even if these were not explicitly indicated. it is possible, for instance, that Hillel's promulgation of the prosbul received its impulse from [this] acknowledged principle... To prevent the Israelites from transgressing one biblical precept, Hillel in effect invalidated another precept.

Paul Heger, The Pluralist Halachah p. 104n
The Sages, though they used hermeneutic rules, were not bound by a particular systematic method, but rather were guided by certain principles they deemed important. The concept of hierarchy among halachic rules, allowing one precept to override another, provided to the Sages a far-reaching philosophical foundation on which to base various rules, even if these were not explicitly indicated. it is possible, for instance, that Hillel's promulgation of the prosbul received its impulse from [this] acknowledged principle... To prevent the Israelites from transgressing one biblical precept, Hillel in effect invalidated another precept.