Reference for Maasrot 5:6

הַמְתַמֵּד וְנָתַן מַיִם בַּמִּדָּה וּמָצָא כְדֵי מִדָּתוֹ, פָּטוּר. רַבִּי יְהוּדָה מְחַיֵּב. מָצָא יוֹתֵר עַל כְּדֵי מִדָּתוֹ, מוֹצִיא עָלָיו מִמָּקוֹם אַחֵר לְפִי חֶשְׁבּוֹן:

One who makes grape-skin wine, and he put water by measure, and he found [afterwards that the wine is] the same measure, he is exempt [from tithes]. Rabbi Yehudah requires [tithing]. If he found more than the measure, he must give [tithes] for it from another place, according to calculation.

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