Shaikh Raslaan (may Allaah preserve him) stated:
When Allaah (The Mighty and Majestic) commanded His slaves to worship Him (alone), He did not leave them to seek a means to this great purpose through any course they want and adopt any means (based on their own) view; rather He legislated worship and legislated its howness (i.e.the manner in which it should be performed), and He precisely determined its form. And anyone who falls short in this or anyone who adds to it, then he is from the transgressors and his deed is rejected. It has been reported in the Saheehayn (i.e. Bukhaari and Muslim) from Aisha (radiyallaahu-anhaa) who said: The Messenger of Allaah (sallal-laahu-alayhi-wasallam) said:
[من أحدث في أمرنا هذا ما ليس منه فهو رد]- Whoever innovates into this affair of ours (i.e. in this religion) that which is not from it will have it rejected.
[فضل العلم -pages 14-15]