Tosefta for Peah 7:2
זַיִת שֶׁנִּמְצָא עוֹמֵד בֵּין שָׁלשׁ שׁוּרוֹת שֶׁל שְׁנֵי מַלְבְּנִים וּשְׁכָחוֹ, אֵינוֹ שִׁכְחָה. זַיִת שֶׁיֶּשׁ בּוֹ סָאתַיִם, וּשְׁכָחוֹ, אֵינוֹ שִׁכְחָה. בַּמֶּה דְבָרִים אֲמוּרִים, בִּזְמַן שֶׁלֹּא הִתְחִיל בּוֹ. אֲבָל אִם הִתְחִיל בּוֹ, אֲפִלּוּ כְּזֵית הַנְּטוֹפָה בִּשְׁעָתוֹ, וּשְׁכָחוֹ, יֶשׁ לוֹ שִׁכְחָה. כָּל זְמַן שֶׁיֶּשׁ לוֹ תַחְתָּיו, יֶשׁ לוֹ בְרֹאשׁוֹ. רַבִּי מֵאִיר אוֹמֵר, מִשֶּׁתֵּלֵךְ הַמַּחֲבֵא:
An olive tree that stands between three rows of two rectangles [of grain], and one forgets it, it is not [subject to] <i>Shikhechah</i>. An olive tree that has two <i>Seah</i> [a specific unit of volume] [of olives remaining] in it, and he forgets it, it is not [subject to] <i>Shikhechah</i>. Regarding when did they say this? When he did not start [picking] it, but if he started, even the olive tree of Netufah in its time, and he forgets it, it is [subject to] <i>Shikhechah</i>. Any time that [the law of <i>Shikhechah</i>] applies under it [the tree], it applies at the top of it; Rabbi Meir says: This is only when the olive-beater has moved on.