(19) باب ائْتِمَامِ الْمَأْمُومِ بِالإِمَامِ
Anas b. Malik reported:
The Messenger of Allah (ﷺ) fell down from a horse and his right side was grazed, and the rest of the hadith is the same with the addition of these words:" When he (the Imam) says prayer standing, you should also do so."
Reference: Sahih Muslim 411 c
In-book reference: Book 4, Hadith 85
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 819