question #1 Sahih Muslim Introduction 38, Introduction, Narration 37 : What is the significance of verifying the reliability of a narrator in Islamic tradition?

‘Indeed Abbād bin Kathīr, about whose condition you are aware, when he related [narrations] he introduced a grave matter- do you believe that it should be said to the people ‘Do not take from him?’ Sufyān said: ‘Indeed!’ Abd Allah [bin al-Mubārak] said: ‘So when I was in an assembly and Abbād was mentioned there, I praised him regarding his Dīn and said: ‘Do not take from him.’Muhammad said, Abd Allah bin Uthmān narrated to us, he said, my father said, Abd Allah bin al-Mubārak said: ‘I ended up in an assembly of Shu’bah, and he said: ‘This is Abbād bin Kathīr so be warned against him.’