"I asked her about the voluntary Salat of Messenger of Allah (S), she said: 'He would pray long into the night standing, and long into the night sitting. So when he recited and he was standing, he would bow and prostrate whole he was standing, and when he recited while he was sitting, he bowed and prostrated while he was sitting.'"
عَنْ صَلاَةِ رَسُولِ اللَّهِ ﷺ عَنْ تَطَوُّعِهِ قَالَتْ كَانَ يُصَلِّي لَيْلاً طَوِيلاً قَائِمًا وَلَيْلاً طَوِيلاً قَاعِدًا فَإِذَا قَرَأَ وَهُوَ قَائِمٌ رَكَعَ وَسَجَدَ وَهُوَ قَائِمٌ وَإِذَا قَرَأَ وَهُوَ جَالِسٌ رَكَعَ وَسَجَدَ وَهُوَ جَالِسٌ