The Prophet ﷺ commanded us to respond to the imam, to love one another, and to greet each other with the salam.
حدثنا محمد بن عثمان أبو الجماهر حدثنا سعيد بن بشير عن قتادة عن الحسن
أمرنا النبي ﷺ أن نرد على الإمام وأن نتحاب وأن يسلم بعضنا على بعض
No references are available.
[Its chain is daif] Ibn Majah collected it in Iqamat al-Salawat, chapter on returning the salam to the imam, no. 921, from the hadith of Qatada with this chain, and I did not find an explicit statement of his hearing it, as noted previously at no. 29. Nevertheless, he graded it sahih at 270, and Dhahabi agreed with him.