[Machine] When the Messenger of Allah ﷺ would sit and recite whatever Allah (glory be to Him) willed, he would continue until he completed thirty or forty verses from the Surah. Then, he would stand and recite them, and then prostrate.
كَانَ رَسُولُ اللهِ ﷺ لَمَّا بَدَّنَ وَثَقُلَ يَقْرَأُ مَا شَاءَ اللهُ ﷻ وَهُوَ جَالِسٌ فَإِذَا غَبَرَ مِنَ السُّورَةِ ثَلَاثُونَ أَوْ أَرْبَعُونَ آيَةً قَامَ فَقَرَأَهَا ثُمَّ سَجَدَ
I never saw the Messenger of Allah ﷺ reciting the Quraan in his prayer at night in sitting condition until he became old. Then he used to sit in it (the prayer) and recite the Quran until forty or thirty verses remained, then he stood and recited them and prostrated himself. (Using translation from Abū Dāʾūd 953)
«كَانَ رَسُولُ اللَّهِ ﷺ لَا يَقْرَأُ فِي شَيْءٍ مِنْ صَلَاةِ اللَّيْلِ جَالِسًا حَتَّى إِذَا دَخَلَ فِي السِّنِّ كَانَ يَقْرَأُ حَتَّى إِذَا بَقِيَ عَلَيْهِ ثَلَاثُونَ أَوْ أَرْبَعُونَ آيَةً قَامَ فَقَرَأَ 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»