The Qur'an is the last divine book, which was revealed from Allah as a declaration and guidance to mankind. It is an explanation of all things and means for men to be rightly guided. In many verses of the Qur'an, it is commanded to obey the prophet of Allah. This is quite a significant point because understanding the Qur'an fully can only be possible with following the Sunnah of the Prophet (salla allahu `alayhi wa sallam).
The Sunnah is the explanation of the Qur'an. It is the creed of ahl-i Sunnah, which has been constituted with collecting true hadiths of the prophet Muhammad (salla allahu `alayhi wa sallam), and interpretation of these hadiths by great scholars in later times.
It's worth dwelling upon a point here. The Sunnah is not a concept that can be dealt with separately from the Qur'an. In the Qur'an, it has been mentioned that the prophet removes heavy burdens, makes rules, teaches the ummah (society) the open and hidden meanings of the Qur'an. As a matter of fact, when we look at the practices of Sunnah, we see that the prophet of Allah gave His companions a lot of information about numerous subjects. This information was then interpreted by scholars of the time, continued to be practised in daily lives and has passed on to us generations to generations.
Allah has informed in the surah Al-e Imran that the Prophet (salla allahu `alayhi wa sallam) had the characteristic of teaching the Qur'an and purifying mankind:
Certainly Allah conferred a benefit upon the believers when He raised among them a Messenger from among themselves, reciting to them His communications and purifying them, and teaching them the Book and the wisdom, although before that they were surely in manifest error. (Surah Al-e Imran, 164)
It would be useful to attract attention to the phrase "teaching the book and the wisdom". Because, It is not possible to understand the Qur'an fully and practise its commands without following the sunnah of the prophet of Allah. Our religion is a whole only with the Qur'an and the Sunnah. At that times when the Qur'an was revealed, the people around the prophet learned and practised the commands of our religion as required by looking at the examples of the prophet. Indeed, the prophet has been an important example with His life, where he practised the commands of the religion, for us to understand the Qur'an.
We can give "salat" (ritual prayers) as a clear example to understanding the commands of the religion. As well known, in Islam, performing salat 5 times a day is an obligation and there are verses giving general information about how to perform it, how to perform ablution (wash). However, we can understand how exactly we should perform prayers only by looking at sunnah. Because there is no detailed information in the verses about the way of praying, what to say in prayer, the way of man and woman's performing the prayer, the degree of importance of the prayers, the details of ablution, what nullifies ablution. We can learn such details only by looking at Sunnah of the Prophet (salla allahu `alayhi wa sallam).
As another example, we can mention the suggestions of the prophet about Friday and the things He said about Friday prayer. Beside the subjects such as speaking that which is best, cleanness, foods, modesty, there are verses in the Qur'an about obligations such as fasting, ablution and hajj (pilgrimage). However, there is no detailed information about those worships in the verses. We learn the detail information about how to perform these worships from the interpretations of the scholars about the words and habits of the Prophet (salla allahu `alayhi wa sallam).
Sunnah has ected the lives of Muslims throughout the history, of all past scholars of Islam, shaping their worships. Since the era of our prophet, which has been hundreds of years, the Muslims have worshipped in compliance with the Sunnah. Worships like praying five times a day, fasting, giving charity and sacrificing have not changed until today as they have been always performed according to the Sunnah. For this reason, starting discussions upon the worships, which have been practised for hundreds of years without change, and speculating about the subjects like time of the prayers, the number of the rakaats (units) are completely unnecessary. All of them are obligatory worships, whose details are described in the Sunnah. As a matter of fact, when we look at the Qur'an, we see many verses in the Qur'an about following the Messenger. In a verse, for example, Allah commands us to obey the Messenger (salla allahu `alayhi wa sallam) as follows:
Surely We have sent you as a witness and as a bearer of good news and as a warner, That you may believe in Allah and His Messenger and may aid him and revere him; and (that) you may declare His glory, morning and evening. Surely those who swear allegiance to you do but swear allegiance to Allah; the hand of Allah is above their hands. Therefore whoever breaks (his faith), he breaks it only to the injury of his own soul, and whoever fulfils what he has covenanted with Allah, He will grant him a mighty reward. (Surah Al-Fath, 8-10)
Whoever obeys the Messenger (salla allahu `alayhi wa sallam), he indeed obeys Allah, and whoever turns back, so We have not sent you as a keeper over them. (Surah An-Nisa, 80)
The point one needs to pay attention in the verses is that they emphasise on the concept of "obeying the Messenger". This point shows us that following the Messenger, in other words following His commands and rules is a worship that Allah brought as an obligation. When we look at the verses, we again see that our prophet has the authority to enjoin and forbid things. For example, the verse ".... and whatever the Messenger gives you, accept it, and from whatever he forbids you, keep back, and be careful of (your duty to) Allah. (Surah Al-Hashr, 7) shows that the prophet may forbid certain things for His ummah, apart from those things that are forbidden in the Qur'an. Besides, it is again informed in the verses that the believers took the matters that they did not understand to the Prophet (salla allahu `alayhi wa sallam) and the prophet judged for them.
Those conducts, on the other hand, such as opposing the Messenger's being a judge, or disrespecting His judgements are described in the verses as "transgression". The certainty of the judgement of our prophet and the need for obeying His judgement is stressed in another verse as follows:
It is not fitting for a Believer, man or woman, when a matter has been decided by Allah and His Messenger to have any option about their decision: if any one disobeys Allah and His Messenger, he is indeed on a clearly wrong Path. (Surah Al-Ahzab, 36)
As seen up to here, Allah commands in His verses a strict obedience to His prophet. For this reason, Islam can only be lived through practising the Sunnah along with the Qur'an. The explanations made in the verses related to this subject are certain. Therefore, putting forward a claim of turning away from the sunnah of the prophet is completely opposite to the essence of the Qur'an.
Imam Malik, one of the greatest Islam scholars, compared the Sunnah of the prophet to the ark of Noah and said : The Sunnah of the Prophet Mohammad (sallallahu `alayhi wa sallam) is like the Ark of Noah. Whoever embarks upon it reaches salvation and whoever refuses is drowned.". The true salvation will be realised only when the creed of ahl-i Sunnah is understood by everybody and prevails in the society.