It wasnarrated that Samurah bin Jundab said:
"The Messenger of Allah(ﷺ) commanded us to greet our Imam with Salam, and to greet oneanother with Salam." (ID)
English reference (ID): Vol. 1, Book 5, Hadith 922 (ID)
Arabic reference (ID): Book 5, Hadith 975 (ID)