All that part of the territory of the United States included within the present limits of the District of Columbia shall be the permanent seat of government of the United States.
4 U.S. Code § 72 - Public offices; at seat of Government
All offices attached to the seat of government shall be exercised in the District of Columbia, and not elsewhere, except as otherwise expressly provided by law.
4 U.S. Code § 71 - Permanent seat of Government
All that part of the territory of the United States included within the present limits of the District of Columbia shall be the permanent seat of government of the United States.
4 U.S. Code § 72 - Public offices; at seat of Government
All offices attached to the seat of government shall be exercised in the District of Columbia, and not elsewhere, except as otherwise expressly provided by law.
Funny, they've been "working from home" for years.