Charles Ellicott Commentary Daniel 10:4

"And in the four and twentieth day of the first month, as I was by the side of the great river, which is Hiddekel," — Daniel 10:4 (ASV)

The twenty-fourth day—After the end of his three weeks’ fast the prophet was on the bank of the Tigris, where he saw the following vision. Hiddekel is the Accadian name of the river. (Compare to Genesis 2:14.) Great river is an epithet usually applied to the river Euphrates, as Genesis 15:18. Daniel was here in the body, and not only in the spirit, as Daniel 8:2.