Our aim in this article is to study the rigidity of complete spacelike hypersurfaces immersed in a weighted Lorentzian product space of the type R 1 × P n f , whose Bakry-Émery-Ricci tensor of the fiber P n is nonnegative and the Hessian of the weighted function f is bounded from below. In this setting, supposing that the weighted mean curvature H f is constant and assuming appropriated constraints on the norm of the gradient of the height function, we prove that such a hypersurface must be a slice of the ambient space. Applications to entire spacelike graphs construct over P n are also given. Our approach is based on a suitable formula for the drift Laplacian of an angle function naturally attached to a spacelike hypersurface jointly with a weak version of the Omori-Yau's generalized maximum principle.