Many of the people of Bid'ah (innovation) disbelieve in the Ahadeeth of the Prophet (sallAllaahu alaihi wa sallam) either partly or in totality...
Imaam Ahmad (rahimahullah) said, "Whoever rejects a Hadeeth of Allah's Messenger (sallAllaahu alaihi wasallam) is on the brink of destruction."
Know, may Allah have mercy on you, the same people who transmitted the statements of the Prophet (sallAllaahu alaihi wa sallam) have also transmitted the Qur`an. No one in their right mind will argue about the authenticity of the Qur`an; so how could the validity of the authentic Sunnah be a matter of debate when they both were transmitted to us by the same people? The Sunnah of the Prophet (sallAllaahu alaihi wa sallam) like the Qur`an is wahee (revelation) from Allah the Most High.
"And he (Muhammad) does not speak of (his own) desire. It is only an Inspiration that is inspired."
Thus, it is obligatory upon every Muslim man and woman to follow the Qur`an and the Sunnah in every aspect of their lives. To further elaborate, the Qur`an like the Hadeeth has a chain of narrators that reaches back to the Prophet (sallAllaahu alaihi wa sallam), who heard it from Jibreel (alaihis salaam), who heard it from Allah Ta'ala. Each recitation has its own authentic chain of narrators....
Subhanak Allaahuma wa bihamdika ash-hadu anlaa illaaha illa anta astaghfiruka wa atubu ilayk
If I said anything correct, then it is from Allaah (subhanahu wa taa'ala), and if I erred, then that is from me and shaytan.