Talmud for Eduyot 4:3
בֵּית שַׁמַּאי אוֹמְרִים, הֶבְקֵר לָעֲנִיִּים, הֶבְקֵר. וּבֵית הִלֵּל אוֹמְרִים, אֵינוֹ הֶבְקֵר, עַד שֶׁיֻּבְקַר אַף לָעֲשִׁירִים כַּשְּׁמִטָּה. כָּל עָמְרֵי הַשָּׂדֶה שֶׁל קַב קַב, וְאֶחָד שֶׁל אַרְבָּעָה קַבִּין, וּשְׁכָחוֹ, בֵּית שַׁמַּאי אוֹמְרִים, אֵינוֹ שִׁכְחָה. וּבֵית הִלֵּל אוֹמְרִים, שִׁכְחָה:
Beth Shammai say: Hefker for the poor is hefker. [If one made (his produce) hefker (i.e., "renounced") for the poor but not for the rich, it has the din of hefker and is not subject to leket, shikchah, and peah or to ma'aser, it being written with respect to leket and peah (Leviticus 19:10): "To the poor man and to the stranger shall you leave them." What is the intent of "them"? To apprise us of another "leaving," i.e., hefker, which is like this. Just as this is to the poor and not to the rich, so, hefker is (i.e., can be) to the poor and not to the rich.] And Beth Hillel say: It is not hefker until it is made hefker to the rich, too, like shemitah, [it being written (Exodus 23:11): "And the seventh year it shall lie fallow and you shall leave it." What is the intent of "and you shall leave it"? To apprise us that there is another "leaving," i.e., hefker, which is like shevi'ith. Just as shevi'ith is for both rich and poor, so, hefker.] If all the sheaves in the field were (the size of) a kav, and one, four kabin, and it were forgotten, Beth Shammai say that it is not shikchah, and Beth Hillel say that it is shikchah. And, similarly, if all the sheaves were two kabin, and one, eight kabin, and he forgot it, it is shikchah. More than this is not shikchah.]