Sunan of Abu Dawood Book 2, Hadith 602

حَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا جَرِيرٌ، وَوَكِيعٌ، عَنِ الأَعْمَشِ، عَنْ أَبِي سُفْيَانَ، عَنْ جَابِرٍ، قَالَ رَكِبَ رَسُولُ اللَّهِ صلى الله عليه وسلم فَرَسًا بِالْمَدِينَةِ فَصَرَعَهُ عَلَى جِذْمِ نَخْلَةٍ فَانْفَكَّتْ قَدَمُهُ فَأَتَيْنَاهُ نَعُودُهُ فَوَجَدْنَاهُ فِي مَشْرَبَةٍ لِعَائِشَةَ يُسَبِّحُ جَالِسًا قَالَ فَقُمْنَا خَلْفَهُ فَسَكَتَ عَنَّا ثُمَّ أَتَيْنَاهُ مَرَّةً أُخْرَى نَعُودُهُ فَصَلَّى الْمَكْتُوبَةَ جَالِسًا فَقُمْنَا خَلْفَهُ فَأَشَارَ إِلَيْنَا فَقَعَدْنَا ‏.‏ قَالَ فَلَمَّا قَضَى الصَّلاَةَ قَالَ ‏ "‏ إِذَا صَلَّى الإِمَامُ جَالِسًا فَصَلُّوا جُلُوسًا وَإِذَا صَلَّى الإِمَامُ قَائِمًا فَصَلُّوا قِيَامًا وَلاَ تَفْعَلُوا كَمَا يَفْعَلُ أَهْلُ فَارِسَ بِعُظَمَائِهَا ‏"‏ ‏.‏

Narrated Jabir ibn Abdullah: The Messenger of Allah (ﷺ) rode a horse in Medina. It threw him off at the root of a date-palm. His foot was injured. We visited him to inquire about his illness. We found him praying sitting in the apartment of Aisha. We, therefore, stood, (praying) behind him. He kept silent. We again visited him to inquire about his illness. He offered the obligatory prayer sitting. We, therefore, stood (praying) behind him; he made a sign to us and we sat down. When he finished the prayer, he said: When the imam prays sitting, pray sitting; and when the imam prays standing, pray standing, and do not act as the people of Persia used to act with their chiefs (i.e. the people stood and they were sitting)