I'm trying to calculate the covariant derivative of a Riemann tensor, and I'm using the following way, but there is some problem in my calculations because my calculations do not match with the calculations mentioned in the research paper.
\begin{align} R_{ijkl} &= g_{im} R^{m}{}_{jkl}\tag1\\ \nabla^{a} R_{ijkl} &= g_{im} \nabla^{a} R^{m}{}_{jkl}\tag2\\ \nabla^{a} R_{ijkl} &= g_{im} g^{ab} \nabla_{b} R^{m}{}_{jkl}\tag3 \end{align} where $\nabla_{b} R^{m}_{jkl}$ I have defined as
\begin{equation} \nabla_{i} R^{j}_{abc} = R^{j}_{abc,i} + \Gamma^{j}_{ik} R^{k}_{abc} - \Gamma^{m}_{ia} R^{j}_{mbc} - \Gamma^{m}_{ib} R^{j}_{amc} - \Gamma^{m}_{ic} R^{j}_{abm} \end{equation}
Can anyone please help me in this regard? Where could be a problem? I'm sure that the definition of riemann= $R^{i}_{jkl}$ is the Riemann tensor.
Thank you.