question #1 Sahih Muslim Introduction 36, Introduction, Narration 35 : What is the significance of verifying the credibility of narrators in the transmission of hadiths?

‘Ibn Awn was asked about the Ḥadīth of Shahr and he was standing at the threshold of the door, so [Ibn Awn] said: ‘Indeed they criticized Shahr, indeed they criticized Shahr’. Muslim, may Allah have mercy on him, said ‘He means- the tongues of men were busy criticizing him’.’