Location: 1519 Fourth Street, NW
Completed in 1960 as the first purpose-built Black Muslim place of worship in Washington, Masjid Mohammad was the successor mosque to Nation of Islam Temple # 4 on Ninth Street, NW. Although no longer affiliated with the Nation of Islam, it continues to serve as the center of activity for DC’s African American Muslim population.
From Cultural Tourism DC.
See their web site here: Masjid Muhammad.
Bates Area Civic Association 
Another cool fact according to the sign on 9th St. about the original location: after the mosque moved to its current location, Malcolm X led the congregation for a short time.