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;
Rashi on Numbers
מקדם לעין ON THE EAST SIDE OF AIN — עין is the name of a place. The boundary went to the east of it, and consequently Ain is within the boundary and was part of the land of Israel.
Rabbeinu Bahya
ומחה על כתף ים כנרת, the word is similar to ימחאו כף, “clapping with one’s hands,” (Psalms 98,8) [i.e. an expression of closeness of two objects, touching].
Rashi on Numbers
וירד הגבול AND THE BOUNDARY SHALL GO DOWN — The more the boundary goes from north to south it goes down more and more.