D.C. Code § 49-506
The jurisdiction of the courts and boards established by this title shall be presumed, and the burden of proof shall rest on any person to oust such courts or boards of jurisdiction in any action or proceedings.
Mar. 1, 1889, 25 Stat. 779, ch. 328
as added Feb. 18, 1909, 35 Stat. 635, ch. 146, § 59
1973 Ed., § 39-706.
1981 Ed., § 39-806.