Allah's Messenger - sallallaahu alaihi wasallam - said, "I have left you upon clear proof, its night is like its day, no one deviates from it except one who is destroyed, and whoever lives (long) from amongst you will see great controversy. So stick to what you know from my Sunnah (example) and the Sunnah of the orthodox, rightly-guided caliphs - cling to that with your molar teeth, and stick to obedience even if it is to an Abyssinian slave, since the believer is like the submissive camel, wherever he is led, he follows." [Ahmed, Hasan]

Abdullah ibn Mas'ood [d.32H] - radiyallaahu anhu - said: "Beware of the (religious) innovations which the people invent, since the Deen (Religion) does not pass out of the hearts all at once - rather Shaytaan introduces innovations for him until he expels Eemaan from the heart; and it will soon happen that the people will abandon the obligatory duties which Allah has made binding upon them - the Prayer, the Fast, the lawful and the prohibited, and speak about their Lord - the Mighty and Majestic. So who ever reaches that time then let him flee." It was said: O Abu Abdur-Rahman, to where? He said: "Not to anywhere, he should flee with his heart and his Deen and not sit with anyone of the people of innovation." [al-Lalikaa'ee]

Abu Hanîfah [d.150H] - rahimahullâh - said: “Stick to the narrations and the way of the Salaf (Predecessors) and beware of newly invented matters, for all of it is innovation.” [as-Suyûtî]

Ahmed ibn Hanbal [d.241H] - rahimahullâh - said: "The Fundamental Principles of the Sunnah with us are: Holding fast to what the Companions of the Messenger of Allah (sallallaahu alaihi wasallam) were upon. And taking them (and their way) as a model to be followed. And the abandonment of (religious) innovations, and every innovation is misguidance." [Usool as-Sunnah]