I needed if possible an document where the proof is done. Considering the Einstein-Maxwell-Scalar Field system, we suppose to obtain from the free divergence of momentum tensor the Maxwell-Klein-Gordon D_\muD^\mu\Phi=0. But by the calculations, I obtained Re(D_\muD^\mu\Phi)=0 and I don't known how to prove that we have also Im(D_\muD^\mu\Phi)=0 to conclude. Many authors use that equation without proving.