There was no D.C., to speak of, at the time of George Washington, who died in 1799. The national capital was first in New York City and then in Philadelphia during Washington's Presidency, with a brief refugee period in Princeton, N.J.
The District of Columbia was authorized by legislation in 1790. John Adams was the first President to reside there (as little as possible) beginning in 1800.
In summary, any Moslems resident, during George Washington's lifetime, in the area that is now D.C. would almost certainly have been plantation slaves.
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