סימן סה סעיף יז

וְאִם הֻקְבַּע הַשַּׁעַר לִתְבוּאָה, יָכוֹל לִקְנוֹת בְּהַקְדָּמַת מָעוֹת כְּפִי הַשַּׁעַר, אַף עַל פִּי שֶׁאֵין לְהַמּוֹכֵר כְּלוּם, שֶׁהֲרֵיאֲפִלּוּ תִּתְיַקֵּר אַחַר כָּךְ הַתְּבוּאָה, אֵין הַלּוֹקֵחַ מַרְוִיחַ בְּמַה שֶּׁהִקְדִּים אֶת הַמָּעוֹת, כֵּיוָן שֶׁהָיָה יָכוֹל לִקְנוֹת אָז תְּבוּאָה בִּמְעוֹתָיו בְּשַׁעַר זֶה. וּמֵאַחַר שֶׁפָּסַק בְּהֶתֵּר, אַף עַל פִּי שֶׁנִּתְיַקְּרָה אַחַר כָּךְ הַתְּבוּאָה, בִּשְׁעַת הַפֵּרָעוֹן, וְאֵינוֹ רוֹצֶה לָתֵת לוֹ אֶת הַתְּבוּאָה שֶׁפָּסַק עָלֶיהָ, יָכוֹל לְשׂוּמָהּ עַל סְחוֹרָה אַחֶרֶת שֶׁיִּתֵּן לוֹ, אוֹ שֶׁיִּתֵּן לוֹ מָעוֹת כַּשׁוּוּי שֶׁל עָתָּה (סִימָן תמ"ה) (וְעַיֵּן בְּקוּנְטְרֵס שַׁעַר דֵּעָה בְּסוֹף הַסֵּפֶר שַׁעַר מִשְׁפָּט סִימָן קע"ה סָעִיף קָטָן ב'. וּדְלֹא כְּמוֹ שֶׁכָּתוּב בְּשֹׁלְחָן עָרוּךְ שֶׁל הַתַּנְיָא סָעִיף כ"ח).

If the market price for grain has been set, one may buy at the market price by advancing money, though the seller does not possess any [grain]; for, even if the price of grain increases afterwards, the buyer derives no profit from his advanced payment, since he could have bought the grain then with his money at the current price. Since the transaction was made according to halakhah, even though there was an increase in the price of grain at the time of payment and the seller does not wish to deliver the grain that was agreed upon, the buyer is permitted to assess substitute goods to be delivered [at a later date];³²A new agreement may be formulated transferring the obligation to other goods at the present price of the grain. For example, if they originally agreed that 100 bushels of wheat will be delivered in six months for the present going price of one dollar per bushel, then, six months hence when the 100 bushels are worth, say 120 dollars, they may strike a new deal and the seller may agree to deliver 120 dollars’ worth of another commodity. or the seller must give him cash value at the present price of the grain.³³Despite the fact that the buyer will be receiving 120 dollars cash in return for the 100 dollars he originally paid. This is allowed because once the obligation has become 120 dollars worth of grain, then it makes no difference whether the buyer collects the grain or the equivalent in cash. (See Kuntres Sha'ar Dei'ah at the end of the Seifer Sha'ar Mishpat Chapter 175, paragraph 2 which disagrees with what is written in Shulchan Aruch of the Tanya, paragraph 28).

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.)