The reward of one who prays sitting due to an excuse

Question:
If a person prays sitting, is there a reduction in the reward of the prayer; and that is due to an illness and severe pains that this praying person feels in his back?

Answer:
If one prays with a valid legal excuse, his prayer is complete, whether he prays sitting or on his side, because he is unable to stand, so his prayer is complete and his reward is complete. The obligatory prayer must be performed standing, but if he is unable, he prays sitting, and if he is unable, he prays on his side, and if he is unable, he prays lying down, and his reward is complete.
As for the voluntary prayer, he may pray sitting, but he gets half the reward. If he prays standing, his reward is complete. If he prays sitting while able to stand, and it is a voluntary prayer, he gets half the reward.

The presenter: May Allah reward you with good.