Joshua 15:4

And they go out to Selmona, and issue at the valley of Egypt; and the termination of its boundaries shall be at the sea: these are their boundaries southward.

From thence it passed toward Azmon, and went out unto the river of Egypt; and the goings out of that coast were at the sea: this shall be your south coast.

and it passed along to Azmon, went out at the brook of Egypt; and the border ended at the sea. This shall be your south border.