Messenger of Allah ﷺ prayed in his house while sitting during his illness and the people prayed behind him standing and he pointed to them to sit down. When he had finished the prayer, he said, "The Imam is to be followed and so when he bows you should bow; and when he lifts his head you should also do the same."  

أَنَّهَا قَالَتْ صَلَّى رَسُولُ اللَّهِ ﷺ فِي بَيْتِهِ وَهْوَ شَاكٍ فَصَلَّى جَالِسًا وَصَلَّى وَرَاءَهُ قَوْمٌ قِيَامًا فَأَشَارَ إِلَيْهِمْ أَنِ اجْلِسُوا فَلَمَّا انْصَرَفَ قَالَ إِنَّمَا جُعِلَ الإِمَامُ لِيُؤْتَمَّ بِهِ فَإِذَا رَكَعَ فَارْكَعُوا وَإِذَا رَفَعَ فَارْفَعُوا  

Messenger of Allah ﷺ fell down from a horse and his right side was either injured or scratched, so we went to inquire about his health. The time for the prayer became due and he offered the prayer while sitting and we prayed while standing. He said, "The Imam is to be followed; so if he says Takbir, you should also say Takbir, and if he bows you should also bow; and when he lifts his head you should also do the same and if he says: Samiʿa l-lahu liman hamidah (Allah hears whoever sends his praises to Him) you should say: Rabbana walakal-Hamd (O our Lord! All the praises are for You.") (See Hadith No. 656 Vol. 1).  

سَقَطَ رَسُولُ اللَّهِ ﷺ مِنْ فَرَسٍ فَخُدِشَ أَوْ فَجُحِشَ شِقُّهُ الأَيْمَنُ فَدَخَلْنَا عَلَيْهِ نَعُودُهُ فَحَضَرَتِ الصَّلاَةُ فَصَلَّى قَاعِدًا فَصَلَّيْنَا قُعُودًا وَقَالَ إِنَّمَا جُعِلَ الإِمَامُ لِيُؤْتَمَّ بِهِ فَإِذَا كَبَّرَ فَكَبِّرُوا وَإِذَا رَكَعَ فَارْكَعُوا وَإِذَا رَفَعَ فَارْفَعُوا وَإِذَا قَالَ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ فَقُولُوا رَبَّنَا وَلَكَ الْحَمْدُ  

(who had piles) I asked Messenger of Allah ﷺ about the praying of a man while sitting. He said, "If he prays while standing it is better and he who prays while sitting gets half the reward of that who prays standing; and whoever prays while Lying gets half the reward of that who prays while sitting."  

أَنَّهُ سَأَلَ نَبِيَّ اللَّهِ ﷺ أَخْبَرَنَا إِسْحَاقُ قَالَ أَخْبَرَنَا عَبْدُ الصَّمَدِ قَالَ سَمِعْتُ أَبِي قَالَ حَدَّثَنَا الْحُسَيْنُ عَنِ ابْنِ بُرَيْدَةَ قَالَ حَدَّثَنِي عِمْرَانُ بْنُ حُصَيْنٍ وَكَانَ مَبْسُورًا قَالَ سَأَلْتُ رَسُولَ اللَّهِ ﷺ عَنْ صَلاَةِ الرَّجُلِ قَاعِدًا فَقَالَ إِنْ صَلَّى قَائِمًا فَهْوَ أَفْضَلُ وَمَنْ صَلَّى قَاعِدًا فَلَهُ نِصْفُ أَجْرِ الْقَائِمِ وَمَنْ صَلَّى نَائِمًا فَلَهُ نِصْفُ أَجْرِ الْقَاعِدِ