Shariah contains 5 kinds of rules:

All Our Actions & the Shariah fall into one of the 5 categories; Wajib (Obligatory) Haram(Forbidden) Recommended(Musthab) Disliked (Makrooh) or Mubah(other than any of the 4)

1. WAJIB: The religious duties performance of which is rewarded and neglect of which is punishable are classified as WAJIB.

2. HARAM : Deeds, doing of which is sinful and punishable and abstinence from them rewardable, are termed as HARAM.

3. MUSTAHAB OR SUNNAT: Such of the rites performance of which is rewardable but their commission is not punishable are termed as SUNNAT.

4. MAKROOH; Those deeds, abstinence from which is rewarded, but committing them is not sinful are termed as MAKROOH.

5. MUBAH : Those deeds which are allowed by the Sheriat, but there is neither reward nor punishment for doing or neglecting them, are called MUBAH.

A Muslim is at liberty to ignore the rule (3) and (4) even without any excuse. But he cannot tamper with a Wajib or Haram