“When the Imam says the Salam, then respond to him.”  

أَنَّ النَّبِيَّ ﷺ قَالَ إِذَا سَلَّمَ الإِمَامُ فَرُدُّوا عَلَيْهِ  

“The Messenger of Allah ﷺ commanded us to greet our Imam with Salam, and to greet one another with Salam.”  

أَمَرَنَا رَسُولُ اللَّهِ ﷺ أَنْ نُسَلِّمَ عَلَى أَئِمَّتِنَا وَأَنْ يُسَلِّمَ بَعْضُنَا عَلَى بَعْضٍ