Midrash for Numbers 34:6

"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).