וְיָרַ֨ד הַגְּבֻ֧ל מִשְּׁפָ֛ם הָרִבְלָ֖ה מִקֶּ֣דֶם לָעָ֑יִן וְיָרַ֣ד הַגְּב֔וּל וּמָחָ֛ה עַל־כֶּ֥תֶף יָם־כִּנֶּ֖רֶת קֵֽדְמָה׃
and the border shall go down from Shepham to Riblah, on the east side of Ain; and the border shall go down, and shall strike upon the slope of the sea of Chinnereth eastward;
Mishnah Eruvin
They measure [the Shabbat limit] only through an expert. If he extended the limit at one point and limited it at another, they observe the place where he extended it. If there was one who made it a greater distance and one who made it a lesser distance, the greater distance is observed. Even a slave and even a female slave are believed when they say, “Thus far is the Shabbat limit”, since the sages did not enact the law in order to be strict but in order to be lenient.