Hadith is integral to the Qur’an, since they are inseparably linked to each other. It is impossible to understand the Qur’an without reference to Hadith. The Qur’an is the message, and the Hadith is the explanation of the message by the Messenger himself. I mention the following points to clarify the issue:
1. The Qur’an makes it abundantly clear that the function of the Messenger is not merely that of a deliveryman who simply delivers the revelation from Allah to us. Rather, he has been entrusted with the most important task of explaining and illustrating the same. This is a point mentioned in a number of verses in the Qur’an (See the Qur’an: 16: 44; 64). Therefore, Hadith explains, clarifies, and removes ambiguities about the Qur’an. Hence, once we reject the Hadith, we may never be able to figure out the whole meaning of the Qur’an.
2. Much of Islam will remain mere abstract concepts without Hadith. We would never know how to pray, fast, pay Zakah, or make pilgrimage without the illustration found in Hadith, for these acts of worship remain as abstract imperatives in the Qur’an.
3. The Qur’an tells us the Prophet (peace and blessings be upon him) has taught not only the Book but also the wisdom (See Qur’an: 96:2; 33:34; 4:113, etc.). As Imam Shafi`i stated, the wisdom mentioned here is the Sunnah of the Prophet (peace and blessings be upon him); so if we were to reject the Hadith, we would be rejecting the Qur’an itself.
4. The Qur’an tells us to obey the Messenger and abide by his decision (See the Qur’an: 4:65; 5:49, etc.) Where do we find such decisions except in the Hadith?
5. Last but not least, the Qur’an orders the faithful to emulate the role model of the Messenger and reckons it as the only way to gain the pleasure of Allah. It is therefore imperative that we look up to his morals and behavior and emulate them in our lives. We can never do so without studying the Hadith. It is most illuminating in this respect to learn that when `A’ishah (may Allah be pleased with her) was asked to describe the character of the Prophet (peace and blessings be upon him), her definitive answer was, “His character was the Qur’an.” In other words, he personified the best ideals and values of the Qur’an. How could we then neglect the Hadith, which alone can lead us to the precise ways in which the Prophet (peace and blessings be upon him) exemplified the Qur’anic ideals?

Having said this, however, we must never fall into the temptation of taking all that is found in the works of Hadith as being authentic or genuine. Hadith at all times must be evaluated by the well established rules of validation as established by the great scholars. Such firm criteria include the following: If a certain hadith is contrary to the well established principles of the Qur’an or sound reason, it must be rejected.