Sunan Ibn Majah, Volume 2, Book 5, Hadith 922 (DarusSalam) ⓘ
It was narrated that Samurah bin Jundab said: “The Messenger of Allah commanded us to greet our Imam with Salam, and to greet one another with Salam.”
حَدَّثَنَا عَبْدَةُ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا عَلِيُّ بْنُ الْقَاسِمِ، أَنْبَأَنَا هَمَّامٌ، عَنْ قَتَادَةَ، عَنِ الْحَسَنِ، عَنْ سَمُرَةَ بْنِ جُنْدُبٍ، قَالَ أَمَرَنَا رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ أَنْ نُسَلِّمَ عَلَى أَئِمَّتِنَا وَأَنْ يُسَلِّمَ بَعْضُنَا عَلَى بَعْضٍ
also referenced under: Hadith 922 (Reference) & Book 5, Hadith 975 (In-Book)