Reference for Peah 3:8

הַכּוֹתֵב נְכָסָיו לְעַבְדּוֹ, יָצָא בֶן חוֹרִין. שִׁיֵּר קַרְקַע כָּל שֶׁהוּא, לֹא יָצָא בֶן חוֹרִין. רַבִּי שִׁמְעוֹן אוֹמֵר, לְעוֹלָם הוּא בֶן חוֹרִין, עַד שֶׁיֹּאמַר הֲרֵי כָל נְכָסַי נְתוּנִין לְאִישׁ פְּלוֹנִי עַבְדִּי חוּץ מֵאֶחָד מֵרִבּוֹא שֶׁבָּהֶן:

If one writes his property over to his slave, he goes out a freeman. If he leaves some land over [for himself], he does not go out as a freeman. Rabbi Shimon says: He is in all cases a freeman unless he says: ‘Indeed, all my property is given to so-and-so, my slave, except for one out of a multitude that is among them [i.e., an unspecified, though tiny, portion].’

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