(16) باب جَوَازِ النَّافِلَةِ قَائِمًا وَقَاعِدًا وَفِعْلِ بَعْضِ الرَّكْعَةِ قَائِمًا وَبَعْضِهَا قَاعِدًا
'Abdullah b. Shaqiq al-'Uqaili reported:
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.
Reference: Sahih Muslim 730 e
In-book reference: Book 6, Hadith 133
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1588