It is narrated on the authority of the Mother of the Believers, Umm ’Abdullah ’Aishah, radiyallahu ’anha, that the Messenger of Allah, sallallahu ’alayhi wasallam, said: "Whosoever introduces into this affair of ours (i.e. into Islam) something that does not belong to it, it is to be rejected." [Al-Bukhari & Muslim]