[Machine] The Messenger of Allah ﷺ used to pray while sitting after he reached old age, until the remaining verses of the Surah were thirty or forty, then he would stand and recite, then he would perform a bow.

كَانَ رَسُولُ اللهِ ﷺ يُصَلِّي جَالِسًا بَعْدَمَا دَخَلَ فِي السِّنِّ حَتَّى إِذَا بَقِيَ عَلَيْهِ مِنَ السُّورَةِ ثَلَاثُونَ أَوْ أَرْبَعُونَ آيَةً قَامَ فَقَرَأَ ثُمَّ رَكَعَ

[Machine] The Prophet ﷺ used to not recite anything from the night prayer while sitting until he reached an older age. And when there remained thirty or forty verses, he would stand and recite them, then he would prostrate.

كَانَ النَّبِيُّ ﷺ لَا يَقْرَأُ فِي شَيْءٍ مِنْ صَلَاةِ اللَّيْلِ جَالِسًا حَتَّى دَخَلَ فِي السِّنِّ وَكَانَ إِذَا بَقِيَتْ عَلَيْهِ ثَلَاثُونَ آيَةً أَوْ أَرْبَعُونَ قَامَ فَقَرَأَهَا ثُمَّ سَجَدَ

"I never saw the Messenger of Allah ﷺ pray sitting down until he grew old. Then he would pray sitting down and when there were thirty or forty verses left, he would stand up and recite them, then bow." (Using translation from Nasāʾī 1649)

«كَانَ رَسُولُ اللَّهِ ﷺ لَا يَقْرَأُ فِي صَلَاتِهِ جَالِسًا حَتَّى دَخَلَ فِي السِّنِّ فَكَانَ يَقْرَأُ وَهُوَ جَالِسٌ فَإِذَا بَقِيَ عَلَيْهِ مِنَ السُّورَةِ ثَلَاثُونَ آيَةً أَوْ أَرْبَعُونَ آيَةً قَامَ فَقَرَأَهَا ثُمَّ رَكَعَ»

"كَانَ رَسُولُ اللهِ ﷺ يُصَلِّي صَلَاةَ اللَّيْلِ قَائِمًا، فَلَمَّا دَخَلَ فِي السِّنِّ جَعَلَ يُصَلِّي جَالِسًا، فَإِذَا بَقِيَتْ عَلَيْه ثَلَاثُونَ آيَةً أَوْ أَرْبَعُونَ آيَةً قَامَ فَقَرَأَهَا ثُمَّ رَكَعَ".