[Nogbad]

Is there contemporaneous documentation on individuals
other than Mohammed from the same general time and place?

Mu'awiyah I (602-680) is the first Caliph whose existence is documented by non-Arabic sources.

[muawiyah]

At the time there were not a lot of "other sources". After all, this was the Dark Ages. Times were tough. Nobody was taking notes! Western Europe had suffered serious depopulation and nobody had any idea if there were even any people left in Eastern Europe.