Is it permissible for one who prays a voluntary prayer sitting down to indicate the bowing and prostration?

Question:
Abu Haytham says: If I pray a voluntary prayer while sitting, am I required to bow and prostrate as I would while standing, or is it permissible for me to merely indicate the bowing and prostration?

Answer:
If you pray a voluntary prayer while sitting, you indicate the bowing and prostration, making the indication for prostration lower than the indication for bowing. Yes.