The Messenger of Allaah (peace and blessings of Allaah be upon him) used to say in his khutbah on Friday: 

The best of speech is the Book of Allaah and the best of guidance is the guidance of Muhammad (peace and blessings of Allaah be upon him). The worst of matters are those which are newly-invented, and every innovation is a going astray.


[Muslim Book4 Hadith1885] 
Al-Nasaa’i added with a jayyid isnaad: “and every going astray will be in the Fire.”