The Ummah has been warned by Rasulullah (Allah bless him and grant him peace) about evil innovations. It is very important that Muslims understand this matter so that they avoid errors and tribulations.
“… The most truthful speech is the Book of Allah. The best way is the way of Muhammad. The worst of things is novelties and every novelty is an innovation and every innovation is misguidance and every misguidance is in the Fire.” (Nasa'i Vol 3 pg 188, hadith 1578)
”(the hadith) refers to what is not in agreement (lam uwafiq) with the Kitab or Sunnah or the actions of the Sahabah (Allah be pleased with them). And this was clarified by his saying, 'Whoever initiates a good practice (sunnah) in Islam gets the reward of it and all those who act upon it after him without diminishing their reward at all. And whoever initiates an evil practice (sunnah) in Islam the sin of it is on him as well as the sin of all those who act upon it after him without diminishing their sin at all.' (Muslim) This indicates the reprehensible and the good of what is innovated and is the basis of this matter. And through Allah comes protection and success.” (Tafsir Qurtubi Vol 2 pg 87)
“Whoever initiates a good practice (sunnah) in Islam gets the reward of it…” to the end in which there is the encouraging of initiating good practices and a warning against starting the baseless and reprehensible. The reason for this speech in this text is what was mentioned before it, “a man came with a money bag so big that his hand could not lift it” and the people followed the example and the merit was great for the one who started the good: the opener of the door of that goodness. This text completely qualifies his (Allah bless him and grant him peace) saying that, “every novelty is innovation and every innovation is misguidance”. It indicates that the intended meaning is baseless novelties and reprehensible innovation. This has been dealt with previously in the book of salat al jumuah where we mentioned that innovation is of five types: necessary, recommended, prohibited, disliked and allowed. (Nawawi's Sharh Sahih Muslim Vol 7 pg 104 )