I asked 'A'isha about the prayer of the Messenger of Allah ﷺ. She said: The Messenger of Allah ﷺ would observe prayer (Nafl) in a standing position as well as in a sitting position, and when he commenced the prayer in a standing position, he bowed in this very position, and when he commenced the prayer in a sitting position, he bowed in this very position.
عَنْ صَلاَةِ رَسُولِ اللَّهِ ﷺ فَقَالَتْ كَانَ رَسُولُ اللَّهِ ﷺ يُكْثِرُ الصَّلاَةَ قَائِمًا وَقَاعِدًا فَإِذَا افْتَتَحَ الصَّلاَةَ قَائِمًا رَكَعَ قَائِمًا وَإِذَا افْتَتَحَ الصَّلاَةَ قَاعِدًا رَكَعَ قَاعِدًا