"I never saw the Messenger of Allah ﷺ offer his voluntary prayers sitting down until one year before his death. Then he used to pray sitting down, reciting the surah so slowly that it seemed to be longer than a surah that is longer."
مَا رَأَيْتُ رَسُولَ اللَّهِ ﷺ صَلَّى فِي سُبْحَتِهِ قَاعِدًا قَطُّ حَتَّى كَانَ قَبْلَ وَفَاتِهِ بِعَامٍ فَكَانَ يُصَلِّي قَاعِدًا يَقْرَأُ بِالسُّورَةِ فَيُرَتِّلُهَا حَتَّى تَكُونَ أَطْوَلَ مِنْ أَطْوَلَ مِنْهَا