Riyad as-Salihin (The Meadows of the Righteous)
by Imam Nawawi
18. Chapter: On the prohibition against innovations and new matters
Allah Almighty says, "And what is there after truth except misguidance?" (10:32)
and the Almighty says, "We have not omitted anything from the Book." (W6:39; H6:38)
The Almighty says, "If you have a dispute about something, refer it back to Allah and the Messenger" (W4:58; H4:59) i.e. the Book and the Sunna,
and the Almighty says, "This is My Path and it is straight, so follow it. Do not follow other ways or you will become cut off from His Way." (W6:154; H6:153)
The Almighty says, "Say: 'If you love Allah, then follow me and Allah will love you and forgive you for your wrong actions," (3:31) and the ayats about this topic are numerous and well-known.
169. 'A'isha said that the Messenger of Allah, may Allah bless him and grant him peace, said, "Anyone who introduces an innovation in this affair of ours which is not part of it, it will be rejected." [Agreed upon]
In a variant of Muslim, "Anyone who does an action which is not in accordance with this affair of ours will be rejected."
170. Jabir said, "While the Messenger of Allah, may Allah bless him and grant him peace, was delivering an address, his eyes would become red, he would raise his voice and he would become very angry until he was like someone admonishing an army. He would say, "(Guard youselves against attack) in the morning and the evening.' He would say, 'I have been sent at a time when I and the Last Hour are like these two,' and he joined together his index finger and middle finger.' He would say, 'Following on from that: the best speech is the Book of Allah. The best guidance is the guidance of Muhammad, may Allah bless him and grant him peace. The worst of matters are the new ones, and every innovation is misguidance.' Then he would say, 'I am more entitled to every believer than his own self. Whoever leaves property, it is for his family. Whoever leaves a debt or family, it is for me and on me." [Muslim]
Al-'Irbad ibn Sariyya has his hadith which is in the Chapter on Following the Sunna (157).