Related for Eruvin 4:3
מִי שֶׁיָּצָא בִרְשׁוּת וְאָמְרוּ לוֹ, כְּבָר נַעֲשָׂה מַעֲשֶׂה, יֶשׁ לוֹ אַלְפַּיִם אַמָּה לְכָל רוּחַ. אִם הָיָה בְתוֹךְ הַתְּחוּם, כְּאִלּוּ לֹא יָצָא, שֶׁכָּל הַיּוֹצְאִים לְהַצִּיל, חוֹזְרִין לִמְקוֹמָן:
If one went out [of the tchum] by sanction [e.g., to testify to (the appearance of) the New Moon or to save one from idolators or from a flood], and he were told: "The deed has already been done" [and there is no need to go], he has two thousand cubits on all sides [from the place where he was told]. If he were within the tchum, it is as if he had not left. [This is what is meant: If those two thousand cubits accorded him on every side from the place where he was told were within the two thousand cubit tchum of his house, it is as if he had not left his tchum, and he may walk to his house and be as before.] For all who leave (the tchum) to rescue, return to their places. [This is what is meant: For we find another lenient ruling vis-à-vis those who leave the tchum to rescue people from idolators of from cave-ins, viz.: Since they left by sanction, they were permitted to return with their arms to their places, and they were not constrained to leave them there. Here, too, they were lenient with those who had left.]