'A'isha reported that the Messenger of Allah ﷺ would pray in the night for a long time, and when he prayed standing be bowed in a standing posture, and when he prayed sitting, he bowed in a sitting posture. (Using translation from Muslim 730b)  

كَانَ رَسُولُ اللهِ ﷺ «يُصَلِّي لَيْلًا طَوِيلًا فَإِذَا صَلَّى قَائِمًا رَكَعَ قَائِمًا وَإِذَا صَلَّى قَاعِدًا رَكَعَ قَاعِدًا»  

"I never saw the Messenger of Allah ﷺ pray sitting down until he grew old. Then he would pray sitting down and when there were thirty or forty verses left, he would stand up and recite them, then bow." (Using translation from Nasāʾī 1649)  

«مَا رَأَيْتُ رَسُولَ اللهِ ﷺ صَلَّى جَالِسًا حَتَّى دَخَلَ فِي السِّنِّ فَكَانَ يُصَلِّي وَهُوَ جَالِسٌ يُقْرَأُ قَاعِدًا فَإِذَا غَبَرَ مِنَ السُّورَةِ ثَلَاثُونَ أَوْ أَرْبَعُونَ آيَةً قَامَ فَقَرَأَهَا ثُمَّ رَكَعَ»