Midrash sa Mga Bilang 34:6: Sifrei Devarim & Yalkut Shimoni

Those (lands) that they conquered outside of Eretz Yisrael — Whence is it derived that those opposite them (that they conquered) in the west are theirs? From (Devarim 11:24) "From the desert and the Levanon, from the river, the river Perath, until the western sea shall be your border." "From the desert"; but the desert (itself) is not your border. But if you conquered (outside of Eretz Yisrael) near the desert, then the desert itself is your border. " from the river"; but the river (itself) is not your border. But if you conquered (outside of Eretz Yisrael) near the river, then the river itself is your border. "until the western sea"; but the sea (itself) is not your border. But if you conquered (outside of Eretz Yisrael near the sea), then the sea itself is your border. And thus is it written (Bamidbar 34:6) "And (what is) the western border? The Great Sea (the Mediterranean) and the bounds (i.e., the islands within it) shall be for you. This shall be the western border for you." We find, then, that every place that those who came up from Bavel seized from Eretz Yisrael until Keziv — (the fruits of shevi'ith) are not eaten and (the land) is not worked. Those who came up from Egypt — (the fruits) are eaten, but (the land) is not worked, (by rabbinical enactment).

"And the boundary shall be the sea." It was taught: What is considered the Land of Israel and what is considered outside the Land? Anything that receives abundant water from the torrents of Ammon and is within the Land [of Israel], it is considered part of the Land. Anything that receives abundant water from the torrents of Ammon but is outside the Land, it is considered outside the Land. And those who are at sea see them as if a thread is stretched over them from Kefarloriya to the Ocean Sea, from the River of Egypt to the Ocean Sea. Within the thread is the Land of Israel, and outside the thread is outside the Land. The rabbis ask: What is the purpose of the phrase "and the boundary shall be the sea"? It is needed for those at sea. But Rabbi Yehuda says it is not necessary for those at sea.