Musnad Ahmad 459:4

Ad-Dahhak ibn Makhlad narrated to us, from Thawr, from Khalid ibn Ma'dan, from Abd al-Rahman ibn 'Amr as-Sulami, from Irbad ibn Sariyah, who said: The Messenger of Allah (ﷺ) led us in the dawn prayer, then he turned to us and delivered an eloquent sermon, because of which eyes shed tears and hearts trembled. We said—or they said—: "O Messenger of Allah, it is as if this is the sermon of one bidding farewell, so advise us." He said: "I advise you to fear Allah (taqwa), and to listen and obey, even if it be an Abyssinian slave. For whoever among you lives after me will see much disagreement. So, you must follow my Sunnah and the Sunnah of the rightly-guided, rightly-directed Caliphs; hold onto it with your molar teeth. And beware of newly invented matters, for every newly invented matter is an innovation (bid'ah), and every innovation is a misguidance."