Originally Posted by Helikido
Allah explicitly tells us to follow the teachings and saying of prophet mohammed s.a.w, like sister noraina posted one of the verses telling us this.
In the Quran it tells us to pray but not how to, thats where the sunnah comes in and tells us how to pray.
There are many other things where the sunnah EXPLAINS and goes into more detail, gives rulings on certain issues
Any rulings or teachings in the sunnah come directly from the Quran and for anybody to deny the sunnah is denying the Quran, as i said before Allah tells us to follow Mohammed s.a.w , he s.a.w said to follow his companions when he passed away, and only some where actually able to give rulings (fatwas)
Just as the Quran has been protected and preserved so have the hadeeths, which go through very rigorous inspections to make sure of their authenticity and are graded upon very strict measures,
They are graded as follows
Sahih - (absolutely authentic, no unbroken chain of narrators, each narrator is a strong narrator, no hidden cause to think hadeeth is weak)
Hasan - not as good as authentic
Dheef - weak (maybe narrator was known to have bad memory or has lied once)
Mawdhu - fabricated or a lie
Shia are completely different and some are considerd kaffir as they curse some of the companions of mohammed s.a.w and his wife Aisha r.a and if this is the case they are kaffir. (Not all are like this but many are known for this)