The Sunnah is the sum of the actions, sayings and moral character of the Prophet Muhammad (s). The Sunnah is the way we learn about his manners, ethics and religious life. But how do we know what the Sunnah is? The way the Sunnah gets transmitted to us is through the hadiths which are chains of oral transmission. 

For practical reasons, the Qur’an cannot contain every single detail of Islam.  

If that were the case, the Qur’an would have had to be thousands of volumes and we all know that that would not have been practical. For this reason, the Sunnah and hadith were essential tools in expanding the meaning of the Qur’an. 

But not all hadiths are equal.  

The hadiths of the Prophet which have been transmitted by the Ahl al-Bayt are the most reliable. Why? Because the Ahl al-Bayt were infallible from mistakes and sins.