The Messenger of Allah ﷺ led us in the dawn prayer, then turned to us and delivered an eloquent admonition that brought tears to our eyes and made our hearts tremble.We said, or they said, "Messenger of Allah, this seems like the admonition of someone bidding farewell, so give us your final counsel."He said, "I urge you to fear Allah, and to listen and obey even if a black slave is placed in authority over you. Whoever among you lives long after me will see much disagreement, so hold fast to my Sunnah and the Sunnah of the rightly guided caliphs. Cling to it with your molars. Beware of newly invented matters, for every newly invented matter is an innovation, and every innovation is misguidance."
حدثنا الضحاك بن مخلد عن ثور عن خالد بن معدان عن عبد الرحمن بن عمرو السلمي
صلى لنا رسول الله ﷺ الفجر ثم أقبل علينا فوعظنا موعظة بليغة ذرفت لها الأعين ووجلت منها القلوب قلنا أو قالوا يا رسول الله كأن هذه موعظة مودع فأوصنا قال أوصيكم بتقوى الله والسمع والطاعة وإن كان عبدا حبشيا فإنه من يعش منكم يرى بعدي اختلافا كثيرا فعليكم بسنتي وسنة الخلفاء الراشدين المهديين وعضوا عليها بالنواجذ وإياكم ومحدثات الأمور فإن كل محدثة بدعة وإن كل بدعة ضلالة
Its isnad is sahih, its men are reliable. Dahhak bin Makhlad is Abu Asim al-Nabil, and Thawr is Ibn Yazid, Abu Khalid al-Himsi, and Khalid bin Madan is more well known than both of them. The hadith has already appeared at 17077.