The Qur'an is the constitution of Islam, and the Sunnah is the law that clarifies the constitution (this is in light of what people are upon today).

The Shaykh : ... when He addressed His Prophet with His saying: So the Sunnah of the Prophet (peace and blessings be upon him) is the complete clarification of the Qur'an, and the Qur'an is the original, the constitution of Islam. As for the Sunnah, it is that which explains and details the Qur'an. This is not by likening Allah to creation, but rather by way of approximation: the Qur'an is like the constitution in earthly systems, and the Sunnah is like the law that clarifies the constitution. Therefore, it is agreed upon by all Muslims that the Qur'an cannot be understood except by the clarification of the Messenger (peace and blessings be upon him). This is a matter of scholarly consensus. However, the point on which Muslims differed, and their effects differed thereafter, is that all the misguided old sects did not raise their heads to this third condition, which is following the righteous predecessors (the Salaf). By doing so, they contradicted the verse I mentioned earlier repeatedly. Then they contradicted the path of Allah, for the path of Allah is one, which is what was mentioned in the previous verse: I said: The Prophet (peace and blessings be upon him) added clarification to this verse...