One day, Messenger of Allah (ﷺ) delivered a very effective speech, as a result, eyes shed tears and hearts became softened. A man said: "O Prophet of Allah! It sounds as if this is a farewell speech, so advise us." He (ﷺ) said, "I admonish you to fear Allah, and to listen and obey even if a black slave has been appointed as your leader. For whoever among you lives after me will see much discord. So hold fast to my Sunnah and the Sunnah of the Rightly-Guided Caliphs who will come after me. Adhere to them and hold fast to them. Beware of Bid'ah (in religion) because every Bid'ah is a misguidance."

[Abu Da wud and At-Tirmidhi].