unfortunately there is no official reference, you have to refer to the respective Regs which apply to:
a) the pilot receiving the FR (which in this particular case is FAR) and
b) (if it's NOT an N-registered aircraft, which makes the situation difficult, otherwise it wouldn't be a big deal) the Regs of the country in which the aircraft being used for the FR is registered.
Which basically means the person (CFI) giving the FR must hold a current FAA CFI in order to be entitled according to the FARs to conduct the FR and endorse the pilots logbook, as well as a valid foreign CFI appropriate to the registration of the aircraft being used, because the pilot receiving the FR (if only FAA certified) is not entitled to act as PIC on an aircraft which is not N-registered outside US territory.