One day the Apostle of Allah (peace and blessings of Allah swt be upon him) led us in prayer, then faced us and gave us a lengthy exhortation at which the eyes shed tears and the hearts were afraid.
A man said: Apostle of Allah! It seems as if it were a farewell exhortation, so what injunction do you give us?
He then said: I enjoin you to fear Allah, and to hear and obey even if it be an Abyssinian slave, for those of you who live after me will see great disagreement. You must then follow my sunnah and that of the rightly-guided caliphs. Hold to it and stick fast to it. Avoid novelties, for every novelty is an innovation, and every innovation is an error.