Revelation 9:14
Saying to the sixth angel which had the trumpet, Loose the four angels which are bound in the great river Euphrates.
Nave's Topical Index—AKJV

Revelation 16:12
And the sixth angel poured out his vial on the great river Euphrates; and the water thereof was dried up, that the way of the kings of the east might be prepared.
Nave's Topical Index—AKJV