בבא בתרא קעד.
"פריעת בעל חוב מצוה"
There was a לוה who died, while still owing money to his מלוה. The guarantor (ערב) on the loan paid off the loan to the מלוה without consulting with the borrower’s יתומים. He now came to get reimbursed from the יתומים for paying the lender. ר' פפא says פריעת בע"ח מצוה and these orphans are minors and not מחוייב במצות. The רשב"ם explains this debt owed to the ערב is a מלוה ע"פ (and he holds שעבודא לאו דאורייתא) so there remains a מצוה to pay it, but since they are currently minors, they are exempt. The ערב will have to wait till they become adults and then claim his reimbursement. רש"י [כתובות פו.] explains, the מצוה to keep one’s word and to pay back debts, is derived from the pasuk "הין צדק" and the Gemara learns שיהא "הן" שלך צדק "ולאו" שלך צדק. The פתחי תשובה [חו"מ ס' צז' אות ד'] quotes the תשובת הרא"ש, that if a לוה swears he will not sell off any of his assets to pay back his מלוה, the שבועה is not חל because he is מושבע ועומד to pay back and we are כופין אותו to pay back his loan. The פתחי תשובה says the pasuk רש"י brings is only an אסמכתא as it is referring to weights and measures. The רמב"ן also holds [קעה: ד"ה ואיכא] פריעת בע"ח is a מצוה דאורייתא, but says the pasuk רש"י brings is discussing not being אחד בפה ואחד בלב. The רמב"ן learns it from "והאיש אשר אתה נושה בו יוציא אליך העבוט", here there is a direct command from the Torah to pay back. The טור [חו"מצג] says if we know the לוה has the money, מכין אותו until he pays back, because פבעח"מ. The מנח"ח [רנט] says,this proves it’s a מצוה דאורייתא because we’re onlyכופה on דאורייתא not דרבנן. ר' חיים was asked (stencils קכ"ט), if פריעת בע"ח מצוה, then since we have a rule when fulfilling a mitzvah, אל יבזבז יותר מחומש, here too, when repaying a loan, which is a mitzvah, one should not have to spend more than a 1/5th of his assets?ר' חיים answers that when the לוה pays back the loan, it’s considered he gave back the Lenders money and not his own. In [ס' תרנו] ביאר הלכה the ח"ח asks why the Gemara asks if a father only has 5 סלעים to his name, but must fulfill פדיון הבן on himself and his son, who takes precedence? If the father only owns 5 selaim he should not have to be מקיים פדיון הבן at all, because of אל יבזבז יותר מחומש?[או"ח ח"ה ס' מא] ר' משה brings this ביאר הלכה and answers with a כלל. If the mitzvah is not מוכרח that one spend money on it, like a Esrog, if one owns one, he need not purchase one. In this type of mitzvah, since the הוצאת כסף is not the עצם מצוה, then we apply אל יבזבז. If the mitzvah is fulfilled דווקא with נתינת כסף, like פדיון הבן then we do not apply אל יבזבז. ר' אלחנן brings the הגהות אשר"י [כתובות אות שיד] that if the father doesn’t leave behind any assets, the יתומים need not pay off the debts, as the חיוב כיבוד אב is only משל אב. If so, even if he does leave behind assets, they should never be מחוייב to pay it back, as it is now theirs?ע"ש . [ועיין שו"ת רע"א קמא סי' סח'].