What is the ruling on praying in a mosque that has a grave within its walls, knowing that there are other mosques further away, which might sometimes lead to missing congregational prayer?

It is not permissible to pray in a mosque that contains a grave, whether the grave was built within the mosque, or introduced into it, or was in the inner courtyard of the mosque. This is because it serves as a pretext for polytheism (shirk), and there are prohibitions against it. However, graves located outside the mosque's boundaries do not prevent prayer. If the courtyard containing the grave is considered part of the mosque, then prayer within it is not permissible. But if it is outside the mosque's designation, then prayer is permissible. If prayer is not permissible (in that mosque), one should go to a more distant mosque to attain the reward of congregational prayer.