In the course of evaluating a Hadeeth's authenticity, scholars of Hadeeth have to investigate each person in its chain(s) of narrators for two things:
- The trustworthiness of their character/uprightness
- The trustworthiness of their memory
The notable exception to this rule is the Sahaba, the first generation of Muslims who were the companions of Prophet Muhammad ﷺ. They are all considered to be trustworthy.
Is there a reason why are they exempted from this check?