Hiddekel.

Daniel 10:4
On the twenty-fourth day of the first month, as I was standing on the bank of the great river, the Tigris,

The Tigris.

Genesis 10:11, 22
From that land he went forth into Assyria, where he built Nineveh, Rehoboth-Ir, Calah, . . .

Genesis 25:18
Ishmael's descendants settled from Havilah to Shur, which is near the border of Egypt as you go toward Asshur. And they lived in hostility toward all their brothers.

Euphrates.

Genesis 15:18
On that day the LORD made a covenant with Abram, saying, "To your descendants I have given this land--from the river of Egypt to the great River Euphrates--

Deuteronomy 1:7
Resume your journey and go to the hill country of the Amorites; go to all the neighboring peoples in the Arabah, in the hill country, in the foothills, in the Negev, and along the seacoast to the land of the Canaanites and to Lebanon, as far as the great River Euphrates.

Deuteronomy 11:24
Every place where the sole of your foot treads will be yours. Your territory will extend from the wilderness to Lebanon, and from the Euphrates River to the Western Sea.

Revelation 9:14
saying to the sixth angel with the trumpet, "Release the four angels who are bound at the great river Euphrates."