Quran and Hadith

For Muslims the first source of guidance in all aspects of life is the Quran, for us is the very words of God. The Quran was transmitted over a period of 23years to the final Messenger on Earth Muhammed SAW. many say why not in one go, was the message transmitted? God points, however the answer is that at the time and for along time man was living in ignorance in Arabia. To the extent for instance  males were burying their own baby daughters alive as they only wanted boys.
God brought forward always a Messenger sometimes with a divine book or sometimes without, bu for the reason of bringing man back onto the right track. When I say right track I mean when man moved away from worshipping God and begun to worship other than God, then God worked in the manner in which he did.
However as with the final Messenger Prophet Muhammed SAW after his demise there are no more Prophets to come until the end of the world. So man now is without any more guidance except by what was revealed to the final Messanger SAW. Infact man is in need of no more guidance  as God has said that all man needs to live on earth and how to live etc is revealed in the Quran.
The Quran therefore is a book of guidance for all.
The second source that Muslims turn to is the Hadith. These are the sayings,actions teaching etc of the Prophet SAW throughout his lifetime.

So to go back a bit as to why the Quran was revealed over this period of 23 years, was for the reason that man was in a state of so much degradation and immorality that if the whole message and guidelines and commands came about in one go and the Prophet SAW taught them to follow and abide by it, they would have refused or ran  away. The message ha dot be given gradually, as it was
In this manner people accepted the message, absorbed it in their lives and Islam spread rapidly throughout the world to become the empire it was and in which the world owes so much.