(20) The Book of Qiyam Al-Lail (The Night Prayer) and Voluntary Prayers During the Day
كتاب قيام الليل وتطوع النهار
(18) Chapter: What is done when one begins the prayer standing and mentioning the differences with those who reported from 'Aisha concerning it
(18) باب كَيْفَ يَفْعَلُ إِذَا افْتَتَحَ الصَّلاَةَ قَائِمًا وَذِكْرِ اخْتِلاَفِ النَّاقِلِينَ عَنْ عَائِشَةَ فِي ذَلِكَ
Sunan an-Nasa'i 1648 
It was narrated from Aishah that :
The Prophet (ﷺ) used to pray when he was sitting. He would recite while sitting, then when there were thirty or forty verses left, he would stand up and recite while standing, then he bowed and prostrated, then he would do likewise in the second rak'ah.
أَخْبَرَنَا مُحَمَّدُ بْنُ سَلَمَةَ، قَالَ حَدَّثَنَا ابْنُ الْقَاسِمِ، عَنْ مَالِكٍ، قَالَ حَدَّثَنِي عَبْدُ اللَّهِ بْنُ يَزِيدَ، وَأَبُو النَّضْرِ، عَنْ أَبِي سَلَمَةَ، عَنْ عَائِشَةَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ يُصَلِّي وَهُوَ جَالِسٌ فَيَقْرَأُ وَهُوَ جَالِسٌ فَإِذَا بَقِيَ مِنْ قِرَاءَتِهِ قَدْرُ مَا يَكُونُ ثَلاَثِينَ أَوْ أَرْبَعِينَ آيَةً قَامَ فَقَرَأَ وَهُوَ قَائِمٌ ثُمَّ رَكَعَ ثُمَّ سَجَدَ ثُمَّ يَفْعَلُ فِي الرَّكْعَةِ الثَّانِيَةِ مِثْلَ ذَلِكَ ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan an-Nasa'i 1648
In-book reference : Book 20, Hadith 51
English translation : Vol. 2, Book 20, Hadith 1649