Hadith 1646
Chapter 18: What is done when one begins the prayer standing and mentioning the differences with those who reported from 'Aisha concerning it - كتاب قيام الليل وتطوع النهار
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ بُدَيْلٍ، وَأَيُّوبَ، عَنْ عَبْدِ اللَّهِ بْنِ شَقِيقٍ، عَنْ عَائِشَةَ، قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي لَيْلاً طَوِيلاً فَإِذَا صَلَّى قَائِمًا رَكَعَ قَائِمًا وَإِذَا صَلَّى قَاعِدًا رَكَعَ قَاعِدًا .
It was narrated that 'Aishah said:
"The Messenger of Allah (ﷺ) used to pray for a long time at night. If he started to pray standing, he would bow standing and if he started to pray sitting, he would bow sitting."
Reference : Sunan an-Nasa'i 1646
In-book reference : Book 20, Hadith 49