סימן סה סעיף ח

צָרִיךְ הַמַּלְוֵה לִזָּהֵר שֶׁלֹּא לֵהָנוֹת מִן הַלֹּוֶה, שֶׁלֹּא מִדַּעְתּוֹ כָּל זְמַן שֶׁמְּעוֹתָיו בְּיָדוֹ, אֲפִלּוּ בְּדָבָר שֶׁהָיָה עוֹשֶׂה לוֹ אַף אִם לֹא הִלְוָהוּ. שֶׁכֵּיוָן שֶׁנֶּהֱנָה שֶׁלֹּא בִּרְשׁוּתוֹ, נִרְאֶה שֶׁסּוֹמֵךְ עָלָיו שֶׁבִּשְׁבִיל מְעוֹתָיו שֶׁבְּיָדוֹ יִמְחַל לוֹ. אֲבָל אִם נֶהֱנָה מִמֶּנּוּ מִדַּעְתּוֹ, מֻתָּר בַּדָּבָר שֶׁהָיָה עוֹשֶׂה לוֹ אַף אִם לֹא הִלְוָהוּ, וּבִלְבַד שֶׁלֹּא יְהֵא דָּבָר שֶׁל פַּרְהֶסְיָא (ק"ס).

The lender must take care not to derive any benefit from the borrower without his permission as long as his money is in the borrower's hands. [This applies] even if it is something that he would have done for him had he not lent him [money], because since he benefits without permission, he (the lender) seems to be assuming that because his money is in (the borrower's) hands, (the borrower) will forgive him. But, when he benefits from him with his permission [then], it is permitted, provided it is something that he would have done for him even had he not lent him money. Another provision is that it is not widely publicized.⁷To summarize: there are three requirements that enable the lender to derive benefit from the borrower while the money is yet on loan: 1) he must first receive permission from the borrower, 2) it must be a favor that the borrower would have done even if the lender had not lent him money, 3) it must be a favor that is not widely publicized.

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.)