From the FAA website:
AIM 1-1-19b3(b) Database Currency (1) In many receivers, an up-datable database is used for navigation fixes, airports and instrument procedures. These databases must be maintained to the current update for IFR operations, but no such requirement exists for VFR use.
AIM 1-1-19f1(b) Equipment and Database Requirements - For IFR Operations "All approach procedures to be flown must be retrievable from the current airborne navigation database..."
AC 90-100, U.S. TERMINAL AND EN ROUTE AREA NAVIGATION (RNAV) OPERATIONS, paragraph 8a(3): The onboard navigation data must be current and appropriate for the region of intended operation and must include the navigation aids, waypoints, and relevant coded terminal airspace procedures for the departure, arrival, and alternate airfields.