Sahih Al Bukhari Hadith Number 732

Narrated Anas bin Malik Al-Ansari: llah’s Messenger (peace be upon him) rode a horse and fell down and the right side of his body was injured. On that day he prayed one of the prayers sitting and we also prayed behind him sitting. When the Prophet (peace be upon him) finished the prayer with Taslim, he said, “The Imam is to be followed and if he prays standing then pray standing, and bow when he bows, and raise your heads when he raises his head; prostrate when he prostrates; and if he says “Sami`a l-lahu liman hamidah”, you should say, “Rabbana wa laka l-hamd.:

10  Call to Prayers (Adhaan)
Hadith number 732
Volume no 1
Chapter: 82 (The necessity of saying the Takbir, i.e., Allahu Akbar (Allah is the Most Great) and the commencement of As-Salat (the prayer)