Can one separate Maaser at a distance from the Tevel to save another from eating Tevel?

Question

I heard a class about the rabbinic prohibition against separating Maaser at a significant distance from the Tevel (שלא מן המוקף). The Rabbi mentioned that one is allowed to violate this prohibition* and separate Maaser at a distance only in order to save someone who is about to eat Tevel, which is a more stringent Torah-prohibition. What is the source for allowing one to violate this rabbinic prohibition in order to save another from the Torah prohibition of eating Tevel?

• _{The obligation to take Maaser Min Hamukaf is Deorayita for Tevel Deorayita. Learned from a Drasha on the verse Bamidbar 18.26. See Tosfot Yevamot 93b and Rishonim there. But if someone makes it at distance, the Teruma is valid, as we see for more examples of incorrect procedures in Temura 5a.}

Answer 1

This is based on the opinion of Rebbi, brought in Eruvin 32a, which is quoted by Rambam in Hilchot Ma’aserot 10:10:

עַם הָאָרֶץ שֶׁאָמַר לְחָבֵר צֵא וְלַקֵּט לִי תְּאֵנִים מִתְּאֵנָתִי אוֹכֵל מֵהֶן הֶחָבֵר עַרְאַי וּמְעַשְּׂרָן [דְּמַאי]. וְאִם אָמַר הֶחָבֵר לְעַם הָאָרֶץ לִלְקֹט לוֹ וְשָׁמַע חָבֵר אַחֵר זֶה הָאַחֵר אוֹכֵל וְאֵינוֹ צָרִיךְ לְעַשֵּׂר שֶׁאֵין הֶחָבֵר מוֹצִיא דָּבָר שֶׁאֵינוֹ מְתֻקָּן מִתַּחַת יָדוֹ וְחֶזְקָתוֹ שֶׁהִפְרִישׁ עָלֶיהָ מִמָּקוֹם אַחֵר. אַף עַל פִּי שֶׁלֹּא נֶחְשְׁדוּ חֲבֵרִים לִתְרֹם שֶׁלֹּא מִן הַמֻּקָּף, כְּדֵי לְסַלֵּק הַמִּכְשׁוֹל מִלִּפְנֵי עַם הָאָרֶץ תּוֹרְמִין:‏

When a common person tells a chavair: "Collect figs for me from my fig tree," the chavair may snack from them and tithe them as one tithes demai.

If a chavair told a common person to gather figs for him and another chavair heard him, the latter may partake [of the figs] without tithing them. [The rationale is that] a chavair will not release produce from his domain unless the appropriate separations were made. [Thus] we can assume that [the owner] separated [terumah and the tithes for this produce] from other [produce]. Although [generally] we do not suspect that a chavair will separate terumah from produce that is not in the same place as the terumah, he may do so to prevent the common person from confronting a spiritual stumbling block.

(Touger translation courtesy of chabad.org)