Hadith 19:

It was narrated that Abu Najeeh al-Irbad ibn Sariyah as-Sulami (r.a) said: The Messenger of Allah (s.a.w) exhorted us, and our hearts trembled and tears flowed from our eyes. We said: O Messenger of Allah, it is as if this is the exhortation of one who is bidding farewell, so instruct us. He said: «I instruct you to fear Allah Azza wa Jalla, and to hear and obey, even if the one who is appointed as your leader is a slave. Those among you who live a long life will see great differences. I urge you to adhere to my Sunnah and the way of the rightly-guided, right-thinking caliphs; adhere firmly to it. Beware of newly invented matters, for every newly invented matter is an innovation, and every innovation is misguidance.»