Reference for Peah 5:2
שִׁבֹּלֶת שֶׁבַּקָּצִיר וְרֹאשָׁהּ מַגִּיעַ לַקָּמָה, אִם נִקְצְרָה עִם הַקָּמָה, הֲרֵי הִיא שֶׁל בַּעַל הַבַּיִת, וְאִם לָאו, הֲרֵי הִיא שֶׁל עֲנִיִּים. שִׁבֹּלֶת שֶׁל לֶקֶט שֶׁנִּתְעָרְבָה בַגָּדִישׁ, מְעַשֵּׂר שִׁבֹּלֶת אַחַת וְנוֹתֵן לוֹ. אָמַר רַבִּי אֱלִיעֶזֶר, וְכִי הֵיאַךְ הֶעָנִי הַזֶּה מַחֲלִיף דָּבָר שֶׁלֹּא בָא בִרְשׁוּתוֹ. אֶלָּא מְזַכֶּה אֶת הֶעָנִי בְּכָל הַגָּדִישׁ, וּמְעַשֵּׂר שִׁבֹּלֶת אַחַת וְנוֹתֵן לוֹ:
An [unharvested] ear of grain [in an area already harvested] the tip of which can touch the standing crop - if it can be harvested with the standing crop, it belongs to the property owner; if not, it belongs to the poor. If an ear of grain that is <i>Leket</i> is intermixed in a stack, one ear must be tithed and given to him [the poor man]. Rabbi Eliezer said: And how does this poor person exchange for something that never came into his possession? Rather, he grants him the entire stack and tithes one ear and gives it to him [and then repossesses the stack].