D.C. Code § 47-1025: Cedar Hill.

When the Frederick Douglass Memorial and Historical Association shall have acquired title in fee simple to the whole or a part, as the case may be, of the property known as Cedar Hill, in the Village of Anacostia, in the District of Columbia, and formerly occupied as the homestead of the late Frederick Douglass, said land and premises shall be, and hereby are declared to be, exempt from all taxes and assessments for taxation so long as the same shall be used for the purposes of this incorporation. Congress reserves the right to amend or repeal this section.