(40) باب الاِئْتِمَامِ بِالإِمَامِ يُصَلِّي قَاعِدًا
It was narrated from Anas bin Malik that the Messenger of Allah (ﷺ) rode a horse and fell from it, and sustained an injury on his rightside. He led one of the prayers sitting, and we prayed behind him sitting. When he had finished he said:
"The Imam is appointed to be followed. If he prays standing then pray standing; when he bows, bow; when he says, Sami' Allahu limanhamidah (Allah hears those who praise Him), say 'Rabbana lakalhamd (Our Lord, to You be praise); and if he prays sitting then pray sitting, all of you."
Reference: Sunan an-Nasa'i 832
In-book reference: Book 10, Hadith 56
English translation: Vol. 1, Book 10, Hadith 833