סימן סה סעיף ז
אִם אֶחָד מַלְוֵה מְעוֹתָיו לַחֲבֵרוֹ עַל זְמַן מָה, כְּדֵי שֶׁיַּחֲזוֹר זֶה וְיַלְוֵהוּ פַּעַם אַחֶרֶת סַךְ יוֹתֵר לִזְמַן כָּזֶה אוֹ סַךְ כָּזֶה לִזְמַן אָרֹךְ יוֹתֵר, זוֹהִי רִבִּית גְּמוּרָה. וְאִם מַלְוֵה לוֹ עַל מְנָת שֶׁיַּלְוֵה לוֹ פַּעַם אַחֶרֶת סַךְ כָּזֶה לִזְמַן כָּזֶה, יֵשׁ אוֹמְרִים שֶׁגַּם כֵּן אָסוּר, וְיֵשׁ אוֹמְרִים דְּמֻתָּר. וְיֵשׁ לְהַחְמִיר. אַךְ אִם לֹא הִתְנוּ כֵּן אֶלָּא שֶׁהוּא מַלְוֵה לוֹ בִּרְצוֹנוֹ פַּעַם אַחֶרֶת, אַף עַל פִּי שֶׁאֵינוֹ עוֹשֶׂה כֵן, אֶלָּא מֵחֲמַת שֶׁזֶּה גַּם כֵּן כְּבָר הִלְוָהוּ, בָּזֶה יֵשׁ לְהָקֵל.
If one lends money to his friend for a specified time, [with the understanding that] [the borrower] reciprocate and lend him at another time, [either] a greater amount for the same period of time or an equivalent amount for a longer period of time, this is absolute ribis. [But,] if he lends him money with the condition [that the borrower] lend him at another time an equivalent amount of money for the same period of time, some say that this, too, is prohibited, and others say that it is permitted.6The explanation of this dispute requires some elaboration. The first opinion maintains that since the original lender is repaid his money and additionally receives the benefit of a loan being made to him, he is, therefore, benefiting from the loan he originally granted and is thus collecting ribis. The second opinion feels that the loan granted in return for the original loan does not constitute a gain to the original lender because he must eventually repay in full, the money that he borrows. It is preferable to adhere to the stringent opinion. However, if no stipulation was made, but he voluntarily lends him money at another time, despite the fact that he is doing this only because the other previously granted him a loan, in this instance one may be lenient.
תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)