The Messenger of Allah ﷺ did not pass away until most of his prayer was performed sitting.
حدثنا أبو قطن حدثنا يونس يعني ابن أبي إسحاق عن أبيه عن الأسود
ما قبض رسول الله ﷺ حتى كان أكثر صلاته جالسا
Its isnad is sahih, and it has already appeared at 26080.