question #1 Sahih Muslim Introduction 83, Introduction, Narration 82 : What is the significance of verifying the authenticity of narrators in Islamic tradition?

‘I heard Abū Nu’aym and he mentioned al-Mu’allā bin Urfān, so [Abū Nu’aym] said, [al-Mu’allā] said: ‘Abū Wā’il narrated to us, he said ‘Ibn Mas’ūd attacked us on the day of Siffīn’. So Abū Nu’aym said: ‘Do you think he was raised after death? [Ibn Mas’ūd passed away in 32 or 33H, several years before the day in question]