סימן סה סעיף א

לְפִי שֶׁנַּפְשׁוֹ שֶׁל אָדָם בְּטִבְעוֹ חוֹמֵד וּמִתְאַוֶּה אֶל הַמָּמוֹן, וְקָרוֹב יוֹתֵר שֶׁיְהֵא הָאָדָם נִכְשָׁל בְּאִסּוּר רִבִּית מִבִּשְׁאַר אִסּוּרִין שֶׁבְּמָמוֹן, כִּי בְּגֶזֶל וְאוֹנָאָה וְכַדּוֹמֶה, הֲרֵי מַשְׁגִּיחַ עַל עַצְמוֹ שֶׁלֹּא יְהֵא נִגְזָל וְשֶׁלֹּא יִתְאַנֶּה, וְגַם זֶה שֶׁהוּא רוֹצֶה לִגְזוֹל אוֹ לְהוֹנוֹת אֶת חֲבֵרוֹ, לִפְעָמִים הוּא נִמְנָע מֵחֲמַת בּוּשָׁה אוֹ מֵחֲמַת יִרְאָה, מַה שֶּׁאֵין כֵּן בְּרִבִּית, כִּי הַלֹוֶה נוֹתֵן לוֹ בִּרְצוֹנוֹ הַטּוֹב, וְהוּא שָׂמֵחַ, כִּי מָצָא מָקוֹם לִלְווֹת עַל כָּל פָּנִים בְּרִבִּית, וְגַם הַמַּלְוֶה חושֵׁב בְּדַעְתּוֹ, כִּי הֲרֵי הוּא עוֹשֶׂה טוֹבָה גְּדוֹלָה עִם הַלֹּוֶה שֶׁיּוּכַל לְהַרְוִיחַ בְּמָמוֹן זֶה כִּפְלֵי כִּפְלַיִם יוֹתֵר מִן הָרִבִּית, וְלָכֵן נָקֵל מְאֹד שֶׁיְהֵא אָדָם נִתְפַּתֶּה חַס וְשָׁלוֹם מִן הַיֵּצֶר הָרַע לִהְיוֹת נִכְשָׁל בְּאִסּוּר זֶה. עַל כֵּן הֶחְמִרָה תוֹרָתֵנוּ הַקְּדוֹשָׁה מְאֹד בְּאִסּוּר זֶה, וְהַרְבֵּה לָאוִין נֶאֶמְרוּ בּוֹ, הַמַּלְוֵה עוֹבֵר בְּשִׁשָּׁה לָאוִין, וְלֹא יָקוּם בִּתְחִיַּת הַמֵּתִים, שֶׁנֶּאֱמַר בְּנֶשֶׁךְ נָתַן וְתַרְבִּית לָקַח וָחָי, לֹא יִחְיֶה. הַלֹּוֶה עוֹבֵר בִּשְׁלשָׁה לָאוִין, הַסּוֹפֵר, וְהָעֵדִים וְהֶעָרֵב עוֹבְרִים כָּל אֶחָד בְּלָאו אֶחָד. וְכֵן הַסַּרְסוּר שֶׁהָיָה בִּינֵיהֶם אוֹ שֶׁסִּיַּע לְאֶחָד מֵהֶם, כְּגוֹן שֶׁהוֹרָה מָקוֹם לְהַלֹּוֶה לִלְווֹת אוֹ שֶׁהוֹרָה מָקוֹם לְהַמַּלְוֵה לְהַלְווֹת, גַּם כֵּן עוֹבֵר בְּלָאו אֶחָד (יו"ד קס).

Preface
The Torah writes: אִם כֶּסֶף תַּלְוֶה אֶת עַמִי אֶת הֶעֳנִי עִמָךְ לאׁ תִהְיֶה לוֹ כְּנוֹשֶׁה לאׁ תְשִׂימוּן עָלָיו נֶשֶׁךְ "When you lend money to my people, to the poor among you, do not press him for payment, do not take interest payment from him" (Ex. 22:24).The Torah obligates us to lend money to one less fortunate than we, but, at the same time, forbids us to derive benefit from making this loan. Any benefit derived thereof is called רִבִּית—interest.There are two major categories of ribis:1) Ribis deoraisa (רִבִּית דְאוֹרַייתָא) i.e. interest that is Scripturally prohibited. The classic case is when the lender stipulates at the time of the loan that the money is being lent with the condition that it be paid back with a set rate of interest. It makes no difference how high or how low the rate may be; in either case, it is ribis deoraisa and the lender must return the interest payment to the borrower. This holds true even where the borrower willingly agreed to the interest payment.2) Ribis derabanan (רִבִּית דְרַבָּנָן), i.e. interest that is Rabbinically prohibited, such as a) sa'ah besa'ah (see para. 11); b) avak ribis (אֲבַק רִבִּית), i.e. "a shade of ribis." The Torah prohibited only interest charged for a loan. The Rabbis added a prohibition on interest charged for a purchase; c) ribis mukdemes (רִבִּית מֻקְדֶמֶת), i.e. "pre-loan" ribis. The borrower sends money or gifts to the lender so that he will lend him money at a later date; d) ribis me'ucheres (רִבִּית מְאֻחֶרֶת), i.e. "post-loan" ribis. The lender did not set interest payments at the time of the loan, but the borrower paid interest at a later date. In cases of ribis derabanan, the Bais Din [Court] does not have the power to force the lender to return the interest collected, but it is, nevertheless, preferable in some cases that he do so on his own.The laws of ribis are complex and this chapter will only touch some of the fundamentals of this important subject. It is, therefore, extremely advisable that when a question of ribis arises, a competent rabbi, well-versed in these laws, should be consulted.
It being the nature of man to desire and lust after money, and it being more likely for man to transgress the prohibition of interest than other prohibitions concerning money, because where robbery and fraud and the like [are concerned], the victim usually protects himself against robbery or fraud. Also, one who wants to rob or defraud another, will often be inhibited because of shame or because of fear. This is not so concerning interest, for the borrower willingly pays and is happy that he has found a place to borrow even with interest. The lender, too, thinks to himself that he is doing a great favor to the borrower by enabling him to profit with this money, many times more than the interest. It is, therefore, very easy for the person to be seduced, Heaven forbid, by his evil inclination to transgress this prohibition. Therefore, the Torah was very stringent with this prohibition. And many prohibitary laws are said concerning it. The lender transgresses six prohibitory laws, and will not be included in the resurrection of the dead, for it is said: "He gave money [in return] for interest and he accepted interest, he shall not live."¹Ezekiel 18: 13. The borrower transgresses three prohibitory laws. The scribe,²Who draws up the loan contract. the witnesses³Who witnesses the loan and sign the contract. and the co-signer each transgress one prohibitory law. [This applies] also [to] the broker who brought them together or if he was of help to one of them, for instance, directing the borrower to one from whom he could borrow, or if he directed the lender to one to whom he could lend, he, too, transgresses one prohibitory law.

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.)