Sunan Ibn Majah Book 5, Hadith 1227

حَدَّثَنَا أَبُو مَرْوَانَ الْعُثْمَانِيُّ، حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ أَبِي حَازِمٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، قَالَتْ مَا رَأَيْتُ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ يُصَلِّي فِي شَىْءٍ مِنْ صَلاَةِ اللَّيْلِ إِلاَّ قَائِمًا حَتَّى دَخَلَ فِي السِّنِّ فَجَعَلَ يُصَلِّي جَالِسًا حَتَّى إِذَا بَقِيَ عَلَيْهِ مِنْ قِرَاءَتِهِ أَرْبَعُونَ آيَةً أَوْ ثَلاَثُونَ آيَةً قَامَ فَقَرَأَهَا وَسَجَدَ ‏.‏

It was narrated that ‘Aishah said:“I did not see the Messenger of Allah (ﷺ) offer any of the night prayers in any way other than standing, until he became old. Then he started to pray sitting down until, when there were thirty or forty Verses left of his recitation, he would stand up and recite them, and prostrate.”