C. F. Keil and Franz Delitzsch on Daniel 10:4-5

Dan 10:4-5 The Theophany. - On the day named Daniel found himself on the side (banks) of the river Hiddekel, i.e., the Tigris (see under Gen 2:14), along with some who accompanied him (Dan 10:7); thus he was there in reality, and not merely in vision as at the Ulai, Dan 8:2. For what purpose he was there is not said. Here he saw a celestial being, whose form is described, Dan 10:5, Dan 10:6. It was a man (אחד, one, not several) clothed in בּדּים, i.e., in a talar of shining white linen (regarding בּדּים, see under Eze 9:2), and his loins girt about with gold of Uphaz. אוּפז occurs nowhere else, except in Jer 10:9 : gold of Uphaz and silver of Tarshish, from which we must conclude that Uphaz is the name of a region, a country, probably only a dialectically different form for אופיר; the combination with the Sanscr. vipâça - Hyphasis is, on the other hand, very far-fetched.