Ash-Shama'il Al-Muhammadiyah, Book 39, Hadith 264 (English) ⓘ

'Abdullah bin Shaqeeq Radiyallahu' 'Anhu reports that he asked 'Aayeshah Radiyallahu 'Anha regarding the nawaafil prayers. She replied: "Rasulullah Sallallahu'Alayhi Wasallam performed nawaafil in the long part of the night whilst standing, and performed nawaafil in the long part of the night whilst sitting. His noble habit was that if he stood and recited (the Qur-aan) he performed ruku' and sajdah in a standing posture. If he recited whilst sitting, he performed the ruku' and sajdah in a sitting posture".

حَدَّثَنَا أَحْمَدُ بْنُ مَنِيعٍ، قَالَ‏:‏ حَدَّثَنَا هُشَيْمٌ، قَالَ‏:‏ حَدَّثَنَا خَالِدٌ الْحَذَّاءُ، عَنْ عَبْدِ اللهِ بْنِ شَقِيقٍ، قَالَ‏:‏ سَأَلْتُ عَائِشَةَ، عَنْ صَلاةِ رَسُولِ اللهِ صلى الله عليه وسلم، عَنْ تَطَوُّعِهِ، فَقَالَتْ‏:‏ كَانَ يُصَلِّي لَيْلا طَوِيلا قَائِمًا، وَلَيْلا طَوِيلا قَاعِدًا، فَإِذَا قَرَأَ وَهُوَ قَائِمٌ رَكَعَ وَسَجَدَ وَهُوَ قَائِمٌ، وَإِذَا قَرَأَ وَهُوَ جَالِسٌ رَكَعَ وَسَجَدَ وَهُوَ جَالِسٌ‏.‏