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.
"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."
"The Messenger of Allah (ﷺ) used to recite sitting, and when he wanted to bow he would stand up for as long as it takes a person to recite forty verses."
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، عَنْ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا هِشَامٌ، عَنِ الْحَسَنِ، عَنْ سَعْدِ بْنِ هِشَامِ بْنِ عَامِرٍ، قَالَ قَدِمْتُ الْمَدِينَةَ فَدَخَلْتُ عَلَى عَائِشَةَ - رضى الله عنها - قَالَتْ مَنْ أَنْتَ قُلْتُ أَنَا سَعْدُ بْنُ هِشَامِ بْنِ عَامِرٍ . قَالَتْ رَحِمَ اللَّهُ أَبَاكَ . قُلْتُ أَخْبِرِينِي عَنْ صَلاَةِ رَسُولِ اللَّهِ صلى الله عليه وسلم . قَالَتْ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ وَكَانَ . قُلْتُ أَجَلْ . قَالَتْ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يُصَلِّي بِاللَّيْلِ صَلاَةَ الْعِشَاءِ ثُمَّ يَأْوِي إِلَى فِرَاشِهِ فَيَنَامُ فَإِذَا كَانَ جَوْفُ اللَّيْلِ قَامَ إِلَى حَاجَتِهِ وَإِلَى طَهُورِهِ فَتَوَضَّأَ ثُمَّ دَخَلَ الْمَسْجِدَ فَيُصَلِّي ثَمَانِيَ رَكَعَاتٍ يُخَيَّلُ إِلَىَّ أَنَّهُ يُسَوِّي بَيْنَهُنَّ فِي الْقِرَاءَةِ وَالرُّكُوعِ وَالسُّجُودِ وَيُوتِرُ بِرَكْعَةٍ ثُمَّ يُصَلِّي رَكْعَتَيْنِ وَهُوَ جَالِسٌ ثُمَّ يَضَعُ جَنْبَهُ فَرُبَّمَا جَاءَ بِلاَلٌ فَآذَنَهُ بِالصَّلاَةِ قَبْلَ أَنْ يُغْفِيَ وَرُبَّمَا يُغْفِي وَرُبَّمَا شَكَكْتُ أَغْفَى أَوْ لَمْ يُغْفِ حَتَّى يُؤْذِنَهُ بِالصَّلاَةِ فَكَانَتْ تِلْكَ صَلاَةُ رَسُولِ اللَّهِ صلى الله عليه وسلم حَتَّى أَسَنَّ وَلَحُمَ - فَذَكَرَتْ مِنْ لَحْمِهِ مَا شَاءَ اللَّهُ - قَالَتْ وَكَانَ النَّبِيُّ صلى الله عليه وسلم يُصَلِّي بِالنَّاسِ الْعِشَاءَ ثُمَّ يَأْوِي إِلَى فِرَاشِهِ فَإِذَا كَانَ جَوْفُ اللَّيْلِ قَامَ إِلَى طَهُورِهِ وَإِلَى حَاجَتِهِ فَتَوَضَّأَ ثُمَّ يَدْخُلُ الْمَسْجِدَ فَيُصَلِّي سِتَّ رَكَعَاتٍ يُخَيَّلُ إِلَىَّ أَنَّهُ يُسَوِّي بَيْنَهُنَّ فِي الْقِرَاءَةِ وَالرُّكُوعِ وَالسُّجُودِ ثُمَّ يُوتِرُ بِرَكْعَةٍ ثُمَّ يُصَلِّي رَكْعَتَيْنِ وَهُوَ جَالِسٌ ثُمَّ يَضَعُ جَنْبَهُ وَرُبَّمَا جَاءَ بِلاَلٌ فَآذَنَهُ بِالصَّلاَةِ قَبْلَ أَنْ يُغْفِيَ وَرُبَّمَا أَغْفَى وَرُبَّمَا شَكَكْتُ أَغْفَى أَمْ لاَ حَتَّى يُؤْذِنَهُ بِالصَّلاَةِ قَالَتْ فَمَا زَالَتْ تِلْكَ صَلاَةُ رَسُولِ اللَّهِ صلى الله عليه وسلم .
" I came to Al-Madinah and entered upon Aishah, may Allah (SWT) be pleased with her. She said: 'Who are you?' I said: 'I am Sa'd bin Hisham bin 'Amir.' She said: 'May Allah have mercy on your father.' I said: 'Tell me about the prayer of the Messenger of Allah (ﷺ).' She said: 'The Messenger of Allah (ﷺ) did such and such.' I said: 'Yes indeed.' She said: 'The Messenger of Allah (ﷺ) used to pray Isha' at night, then he would go to his bed and sleep. In the middle of the night, he would get up to relieve himself and go to his water for purification and perform wudu. Then he went into the Masjid and prayed eight rak'ahs. I think he made the recitation, bowing and prostration equal in length. Then he prayed one rak'ah of witr, then he prayed two rak'ahs sitting down. Then he lay down on his side. Sometimes Bilal would come and tell him that it was time to pray before he napped, and sometimes he napped. And sometimes I was not sure if he had napped or not before he told him that it was time to pray. This is how the Messenger of Allah (ﷺ) used to pray until he grew older and gained weight"- and she mentioned whatever Allah (SWT) willed about his gaining weight. She said: "And the Prophet (ﷺ) used to lead the people in praying witr, then he would go to his bed. In the middle of the night, he would get up and go to water for purification, and to relieve himself, then he would perform wudu. Then he would go into the masjid and pray six rak'ahs, and I think he made the recitation, bowing, and prostration equal in length. Then he prayed one rak'ah of witr, then he prayed two rak'ahs sitting down. Then he lay down on his side. Sometimes Bilal would come and tell him that it was time to pray before he napped, and sometimes he napped. And sometimes I was not sure if he had napped or not before he told him that it was time to pray." She said: "And this is how the Messenger of Allah (ﷺ) continued to pray."
"The Messenger of Allah (ﷺ) did not refrain from (kissing) my forehead when he was fasting, and he did not die until most of his prayers were offered sitting down." Then she said something to the effect that (referred to the prayers) other than the obligatory prayers. "And the dearest of actions to him was that in which a person persists, even if it is little."
"The Messenger of Allah (ﷺ) did not pass away until most of his prayers were offered sitting down, except for the obligatory prayers, and the dearest of actions to him were those which were done persistently, even if they were few."
"By the One in Whose Hand is my soul. The Messenger of Allah (ﷺ) did not pass away until most of his prayers were offered sitting down, except for the obligatory prayers, and the dearest of actions to him were those which were done persistently, even if they were few."