יורה דעה קס״בYoreh De'ah 162

Se’if 1א׳

אָסוּר לִלְוֹת סְאָה בִּסְאָה, אֲפִלּוּ לֹא קָצַב לוֹ זְמַן לְפֵרָעוֹן. וְכֵן כָּל דָּבָר, חוּץ מִמַּטְבֵּעַ כֶּסֶף הַיּוֹצֵא אָז בְּהוֹצָאָה, דְּשֶׁמָּא יִתְיַקְּרוּ, וְנִמְצָא שֶׁנּוֹתֵן לוֹ יוֹתֵר מִמַּה שֶּׁהִלְוָהוּ, אִם לֹא שֶׁיַּעֲשֶׂנּוּ דָּמִים, שֶׁאִם יִתְיַקְּרוּ יִתֵּן לוֹ אוֹתָם הַדָּמִים. וְאִם לֹא עֲשָׂהוּ דָּמִים, וְנִתְיַקְּרוּ, נוֹתֵן לוֹ הַדָּמִים שֶׁהָיוּ שָׁוִים בִּשְׁעַת הַלְוָאָה, וְאִם הוּזְלוּ נוֹתֵן לוֹ הַסְאָה שֶׁהִלְוָהוּ. הַגָּה: יֵשׁ מִי שֶׁכָּתַב דְּבַזְּמַן הַזֶּה מַטְבֵּעַ שֶׁל זָהָב דִּינוֹ כְּכֶסֶף וְלוֹוִין זָהוּב בְּזָהוּב, וְכֵן נוֹהֲגִין לְהָקֵל וְאֵין לִמְחוֹת בְּיָדָם, כִּי יֵשׁ לָהֶם עַל מִי שֶׁיִּסְמֹכוּ. (פִּסְקֵי מהרא"י סי' נ"ד) יֵשׁ מִי שֶׁאוֹמֵר, דְּמֻתָּר לִלְוֹת כִּכַּר לֶחֶם בְּכִכַּר לֶחֶם, כְּמַטְבֵּעַ שֶׁל כֶּסֶף, דְּמֵאַחַר דְּדָבָר מֻעָט הוּא, לֹא קָפְדֵי בְּנֵי אָדָם לַהֲדָדֵי בָּזֶה. (הַטּוּר וְהַרְבֵּה פּוֹסְקִים ועי' בֵּית יוֹסֵף). וְכֵן נוֹהֲגִין לְהָקֵל.

It is forbidden to borrow a se'ah for a se'ah, even where he did not fix him a term for repayment. And so with everything, apart from a silver coin that is then current in expenditure — for perhaps they will become dearer, and it turns out that he gives him more than he lent him — unless he makes it a matter of money, so that if they become dearer he gives him that money. And if he did not make it a matter of money and they became dearer, he gives him the money that they were worth at the time of the loan; and if they became cheaper, he gives him the se'ah that he lent him. Hagah [Rema]: There is one who wrote that in this time a coin of gold has the law of silver, and they borrow a gold piece for a gold piece; and so they are accustomed to be lenient, and one is not to protest against them, for they have upon whom to rely. (Piskei Maharai, siman 54) There is one who says that it is permitted to borrow a loaf of bread for a loaf of bread, like a coin of silver, since it is a small matter and men are not particular with one another in this. (the Tur and many poskim, and see the Beit Yosef) And so they are accustomed to be lenient.

Se’if 2ב׳

אִם יֵשׁ לוֹ מְעַט מֵאוֹתוֹ הַמִּין, אֲפִלּוּ אֵין הַמַּפְתֵּחַ בְּיָדוֹ, לֹוֶה עָלָיו כַּמָּה סְאִין לִפְרֹעַ סְאָה בִּסְאָה. וְאִם אֵין לוֹ כְּלוּם מֵאוֹתוֹ הַמִּין, יִתֵּן לוֹ הַמַּלְוֶה מְעַט מֵאוֹתוֹ הַמִּין אוֹ יַלְוֵהוּ לוֹ, וְאַחַר כָּךְ יַלְוֶה לוֹ כַּמָּה סְאִין (ד"ע דְּלֹא כְּתַלְמִידֵי רַשְׁבָּ"א). הַגָּה: הָיָה לַלֹּוֶה מְעַט מֵאוֹתוֹ הַמִּין פִּקָּדוֹן בְּיַד אַחֵר, הֲרֵי זֶה כְּאִלּוּ הָיָה בְּיָדוֹ. אֲבָל אִם אֲחֵרִים חַיָּבִים לוֹ, לֹא מִקְּרֵי יֵשׁ לוֹ. (בֵּית יוֹסֵף וְכֵן מַשְׁמַע בַּגְּמָרָא דְּאֵיזֶהוּ נֶשֶׁךְ). וְכֵן אִם יֵשׁ לוֹ בְּמָקוֹם אַחֵר וְאֵין לַמַּלְוֶה דֶּרֶךְ לְשָׁם. (הַגָּהוֹת מָרְדְּכַי). לֹוֶה שֶׁאָמַר שֶׁיֵּשׁ לוֹ מְעַט מִזֶּה הַמִּין, יוּכַל הַמַּלְוֶה לְהַלְווֹת לוֹ וְאֵינוֹ צָרִיךְ רְאָיָה לִדְבָרָיו. (שָׁם בְּשֵׁם ר"ח). הָא דְּמֻתָּר לְהַלְווֹת לוֹ כְּשֶׁיֵּשׁ לוֹ מֵאוֹתוֹ הַמִּין, הַיְנוּ סְתָם, אֲבָל אִם הַמַּלְוֶה מַתְנֶה, שֶׁאִם יִתְיַקְּרוּ חִטִּים יְשַׁלֵּם לוֹ חִטִּים, וְאִם יוּזְלוּ יִתֵּן לוֹ מָעוֹת דְּמֵי שָׁוְיָן כַּשַּׁעַר שֶׁל עַכְשָׁו, אָסוּר דְּהָוֵי קָרוֹב לְשָׂכָר וְרָחוֹק לְהֶפְסֵד (ריב"ש סִימָן י"ט).

If he has a little of that kind, even if the key is not in his hand, he borrows upon it as many se'ahs as he likes, to repay a se'ah for a se'ah. And if he has nothing at all of that kind, the lender shall give him a little of that kind or lend it to him, and afterwards he may lend him as many se'ahs as he likes (his own opinion, not in accordance with the disciples of the Rashba). Hagah [Rema]: If the borrower had a little of that kind as a deposit in the hand of another, this is as though it were in his hand. But if others owe it to him, it is not called having it. (Beit Yosef, and so it is implied in the Gemara of "Which is interest") And likewise if he has it in another place and the lender has no way to get there. (Hagahot Mordechai) A borrower who said that he has a little of this kind — the lender may lend to him, and he does not need proof for his words. (ibid., in the name of Rabbeinu Chananel) This, that it is permitted to lend to him when he has of that kind, is in the ordinary case; but if the lender stipulates that if wheat becomes dearer he shall pay him wheat, and if it becomes cheaper he shall give him money to the value it is worth at the present rate, it is forbidden, for it is near to gain and far from loss (Rivash, siman 19).

Se’if 3ג׳

הָיָה לְאוֹתוֹ מִין שַׁעַר בַּשּׁוּק, קָבוּעַ וְיָדוּעַ לִשְׁנֵיהֶם, מֻתָּר לִלְוֹת סְאָה בִּסְאָה. הַגָּה: וְע"ל סִימָן קע"ה אֵיזֶה מִקְרֵי שַׁעַר קָבוּעַ. וְהָא דְּיָכוֹל לִלְוֹת עַל שַׁעַר שֶׁבַּשּׁוּק, הַיְנוּ דְּהַלֹּוֶה יָכוֹל לִפְרֹעַ לוֹ אֵימַת שֶׁיִּרְצֶה, אֲבָל אִם הִתְנָה שֶׁלֹּא יְקַבֵּל פֵּרָעוֹן עַד שְׁעַת הַיֹּקֶר, אָסוּר. (הָרֹא"שׁ בִּתְשׁוּבָתוֹ וּסְמַ"ק וְכָל בּוֹ).

If that kind had a market rate that was fixed and known to them both, it is permitted to borrow a se'ah for a se'ah. Hagah [Rema]: And see below, siman 175, what is called a fixed rate. And this, that he may borrow at the rate that is in the market, is where the borrower may repay him whenever he wishes; but if he stipulated that he would not receive repayment until the time when the price is high, it is forbidden. (the Rosh in his responsum, and the Semak, and Kol Bo)