question #1 Sahih Muslim Introduction 73, Introduction, Narration 72 : What is the significance of verifying the authenticity of a hadith narrator in Islamic tradition?

‘I narrated to Hammād bin Salamah [bin Dīnār al-Basrī], on authority of Sālih al-Murrī , a Ḥadīth on authority of Thābit [bin Aslam al-Banānī], then [Hammād] said: ‘[Sālih] lied’. I also narrated to Hammām on authority of Sālih al-Murrī a Ḥadīth then [Hammām] said: ‘[Sālih] lied’.