The Prophet ﷺ did not pass away until he was performing much of his prayer while seated.
أخبرنا الحسن بن محمد عن حجاج عن ابن جريج قال أخبرني عثمان بن أبي سليمان أن أبا سلمة أخبره أن
أن النبي ﷺ لم يمت حتى كان يصلي كثيرا من صلاته وهو جالس
Muslim reported it in "Prayer of the Traveler," chapter "Permissibility of Voluntary Prayer While Standing or Sitting," etc., hadith 116/732, from the hadith of Hajjaj bin Muhammad with this same account, and it is also found in Kubra, hadith 1360.