It has been taught otherwise: "Leaven shall not be found in your houses" — what does Scripture teach? Because it says, "And no chametz shall be seen with you, and no leaven shall be seen with you," your own you may not see, but you may see that of others and that of the Sanctuary. One might think one may hide it away or accept deposits from gentiles; Scripture says, "shall not be found." From this I know only a gentile whom you have subdued and who dwells with you in the courtyard; a gentile whom you have not subdued and who does not dwell with you in the courtyard, from where? Scripture says, "shall not be found in your houses" — in any case. From this I know only houses; pits, ditches, and caves, from where? Scripture says, "in all your border." And still I might say: in houses one transgresses under "shall not be seen," "shall not be found," "shall not hide it," and "shall not accept deposits," but in the borders, your own you may not see, yet you may see that of others and of the Sanctuary. From where do we apply what is said of one to the other and of the other to this? Scripture says "leaven, leaven" for a verbal analogy: leaven is stated regarding houses and leaven is stated regarding borders, and so on. Rava said: in truth, do not reverse it; it stands upon the opening clause — your own you may not see, but you may see that of others and of the Sanctuary. From this I know only a gentile whom you have not subdued, and so on, until Scripture says, "shall not be found." This teacher returns from the permission and takes the verse for prohibition, because of the doubled "with you, with you." The master said: one might think one may hide it away; Scripture says, "shall not be found." But you said at the outset, you may see that of others. This is no difficulty: this case is where he accepted responsibility for it, and that case where he did not, as Rava said to the people of Mechoza, and so on. The Rabbis taught: a gentile who entered the courtyard of an Israelite with his dough in his hand, the Israelite need not destroy it; but if he deposited it with him, he must destroy it, as it says, "shall not be found." Rav Papa said: it stands on the opening clause. Rav Ashi said: it stands on the closing clause, as it says, "shall not be found" — and this is not his own; and even though hire does not effect acquisition, here it is different, since the Merciful One expressed it in the language of "shall not be found," meaning whatever is found in his hand — this excludes that which is not found in his hand, for that corner is lent to the gentile.
Your Own Chametz You May Not Keep But Another's You May
Yalkut Shimoni on Torah 203:1
תַּנְיָא אִידָךְ, שְׂאֹר לֹא יִמָּצֵא בְּבָתֵּיכֶם, מַה תַּלְמוּד לוֹמַר, לְפִי שֶׁנֶּאֱמַר ["וְ]לֹא יֵרָאֶה לְךָ חָמֵץ וְלֹא יֵרָאֶה לְךָ שְׂאֹר", שֶׁלְךָ אֵי אַתָּה רוֹאֶה אֲבָל אַתָּה רוֹאֶה שֶׁל אֲחֵרִים וְשֶׁל גָּבוֹהַּ. יָכוֹל יַטְמִין וִיקַבֵּל פִּקְדוֹנוֹת מִן הַגּוֹיִם, תַּלְמוּד לוֹמַר לֹא יִמָּצֵא. אֵין לִי אֶלָּא בְּגוֹי שֶׁכְּבַשְׁתּוֹ וְשָׁרוּי עִמְּךָ בֶּחָצֵר, גּוֹי שֶׁלֹּא כְּבַשְׁתּוֹ וְאֵין שָׁרוּי עִמְּךָ בֶּחָצֵר מִנַּיִן, תַּלְמוּד לוֹמַר לֹא יִמָּצֵא בְּבָתֵּיכֶם, מִכָּל מָקוֹם. אֵין לִי אֶלָּא בְּבָתִּים, בְּבוֹרוֹת שִׁיחִין וּמְעָרוֹת מִנַּיִן, תַּלְמוּד לוֹמַר (שם) "בְכָל גְּבֻלֶךָ". וַעֲדַיִן אֲנִי אוֹמֵר בַּבָּתִּים עוֹבֵר מִשּׁוּם בַּל יֵרָאֶה וּבַל יִמָּצֵא וּבַל יַטְמִין וּבַל יְקַבֵּל פִּקְדוֹנוֹת, בִּגְבוּלִין שֶׁלְּךָ אִי אַתָּה רוֹאֶה אֲבָל אַתָּה רוֹאֶה שֶׁל אֲחֵרִים וְשֶׁל גָּבוֹהַּ, מִנַּיִן לִתֵּן הָאָמוּר שֶׁל זֶה בָּזֶה וְשֶׁל זֶה בָּזֶה, תַּלְמוּד לוֹמַר שְׂאֹר שְׂאֹר לִגְזֵרָה שָׁוָה, נֶאֱמַר שְׂאֹר בְּבָתִּים וְנֶאֱמַר שְׂאֹר בִּגְבוּלִין וְכוּ'. רָבָא אָמַר, לְעוֹלָם לֹא תֵּיפוּךְ, וְאֲרֵישָׁא קָאי, שֶׁלְּךָ אִי אַתָּה רוֹאֶה אֲבָל אַתָּה רוֹאֶה שֶׁל אֲחֵרִים וְשֶׁל גָּבוֹהַּ. אֵין לִי אֶלָּא בְּגוֹי [שֶׁלֹּא] (ש)כְּבַשְׁתּוֹ (וְכוּ' עַד), תַּלְמוּד לוֹמַר לֹא יִמָּצֵא. הַאי תַּנָא מֵהֲדַר אֲהֶתֵּירָא וְנָסַב לְמִקְרָא לְאִסּוּרָא, מִשּׁוּם לְךָ לְךָ תְּרֵי זִמְנֵי. אָמַר מַר, יָכוֹל יַטְמִין, תַּלְמוּד לוֹמַר לֹא יִמָּצֵא. וְהָאַמְרֵת רֵישָׁא אֲבָל אַתָּה רוֹאֶה שֶׁל אֲחֵרִים. לֹא קַשְׁיָא, הָא דְּקַבִּיל עָלֵיהּ אַחְרָיוּת וְהָא דְּלָא קַבִּיל, כִּי הָא דְאָמַר רָבָא לִבְנֵי מְחוֹזָא וְכוּ'. תָּנוּ רַבָּנָן גּוֹי שֶׁנִּכְנַס לַחֲצֵרוֹ שֶׁל יִשְׂרָאֵל וּבְצֵקוֹ בְּיָדוֹ אֵין זָקוּק לְבַעֵר, הִפְקִידוֹ אֶצְלוֹ צָרִיךְ לְבַעֵר, שֶׁנֶּאֱמַר לֹא יִמָּצֵא. רַב פָּפָּא אָמַר, אֲרֵישָׁא קָאי. רַב אַשִׁי אָמַר, אַסֵיפָא קָאי, שֶׁנֶּאֱמַר לֹא יִמָּצֵא, וְהָאי לָאו דִידֵיהּ הוּא, וְאַף עַל גַּב דִּשְׂכִירוּת לֹא קַנְיָא שַׁאְנִי הָכָא דְּאַפְקֵיהּ רַחֲמָנָא בִּלְשׁוֹן לֹא יִמָּצֵא, מִי שֶׁמָּצוּי בְּיָדוֹ, יָצָא זֶה שֶׁאֵין מָצוּי בְּיָדוֹ, שֶׁהֲרֵי אוֹתָהּ זָוִית שְׁאוּלָה לְגוֹי.