Sahih Bukhari
Actions while Praying
Volume: 002 / Book Number: 022 / Hadith Number: 328
Narrated 'Aisha the wife of the Prophet:
Allah's Apostle during his illness prayed in his house sitting, whereas some people followed him standing, but the Prophet beckoned them to sit down. On completion of the prayer he said, "The Imam is to be followed. So, bow when he bows, and raise your head when he raises his head." (See Hadith No. 657 Vol 1 for taking the verdict).