What is the ruling on burying the deceased in the mosque courtyard, given the presence of a separating wall, based on his will after he had built the mosque?

If the courtyard of the mosque is within the boundaries of the endowment (waqf), then burial in it is impermissible. This is because it has exited the ownership of the endower and become designated for the mosque, and burial is not permissible in mosques. However, if the courtyard is not included in the endowment and was owned by the testator, or not owned by anyone, then there is no objection to fulfilling the will by burying in it, especially if it is separate from the mosque.