The Qur’an is the ultimate source of Islamic law. It sets the general principles on how we should understand the law. It sets the ethical and moral paradigms of what is acceptable and what is not acceptable behavior.  

For example, the Qur’an rules against stealing the property of orphans or forcing women into prostitution. These rules are important for they set the parameters of how far we can interpret Islamic law. So if we take these two examples, we know that any interpretation that would somehow legalize forced prostitution or theft of an orphan’s property would be totally invalid. 

Knowledge of the Qur’an is essential in understanding Islamic law, especially in our modern world. We often see extremists committing many barbaric acts and justifying them through a warped understanding of Islamic law.  

 But any in-depth reading of the Qur’an, and careful consideration of the moral and ethical principles that it preaches will make one quickly realize how unislamic the behavior of some violent extremists are.  

The Qur’an, however, does not contain all of Islamic law. As we said, it sets the general principles, especially moral and ethical principles, which guide the law. For example, the Qur’an asks us to pray, but it does not tell us how many units of prayer we should perform. Similarly, it tells us to fast, but it does not give us the details as to how to fast.  

So where are we supposed to get these details from? They are to be taken from the hadiths of the Messenger of God (s) and his Ahl al-Bayt (as). These hadiths give us the details, and the Qur'an gives us the general principles.