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.
أَنَّ النَّبِيَّ ﷺ 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