Sayyidina Irbad ibn Sariyah (RA) reported that Allah’s Messenger (SAW) delivered a sermon to them one day after the Salah of Fajr: an eloquent admonition that brought tears to the eyes and fear to the heart. A man submitted, ‘This is the advice of one taking leave. What do you advice us, 0 Messenger of Allah (SAW) ?” He said, “I instruct you to obsorve Taqwa, to listen and to obey even if a black slave (rules you). Those of you who survive will see many discords. Beware; refrain from innovations in religion, for that is error. So, he of you who encounters that must adhere to my sunnah and the sunnah of the rightly guided caliphs. All of you should hold that firmly with your teeth.”
[Ahmed 17145,Abu Dawud 4607,Ibn Majah 42]