Actually, some people claim that the Qur’an is so inclusive that there is no need for the Sunnah (the Prophetic Tradition). They support their claim by citing the Qur’anic verse, “…And We have sent down to you the Book (the Qur’an) as an exposition of everything” (16: 89)
However, this claim is completely wrong and rejected by the Qur’an itself. Allah Almighty says: ” .. And We have sent down unto you (O Muhammad, peace be upon him) the Dhikr [reminder and the advice (i.e. the Qur’an)], that you may explain clearly to men what is sent down to them, and that they may give thought.” (16: 44)
In addition, Allah declares that obeying the Prophet is obligatory, as it is part of obedience to Him (See: 3: 31; 4: 80; 33: 36; 47: 33; etc.) Therefore, it is not proper for a Muslim who knows Islamic law to say that following the Sunnah of the Prophet (peace be upon him) is not required.
By and large, the Qur’an sets the general rules without details. For example, there is no mention in the Qur’an that there are five obligatory prayers to be performed daily. Nor is the number of rakahs of each prayer specified, as well as the percentage of wealth to be paid in Zakah; the details in the rituals of Haj, and other such ordinances and dealings.
All of these details are elaborately dealt with in the Sunnah.