Killing vector preserves scalar curvature

Every Killing vector field $K$ preserves the scalar curvature: ${\mathcal{L}}_{K}R=K^{\alpha }{\nabla }_{\alpha }R=0$. One index proof rewrites this derivative as a doubly contracted curvature commutator acting on the antisymmetric tensor ${\nabla }_{[\mu }{K}_{\lambda ]}$; both terms vanish by symmetry of the Ricci tensor.