question #1 Sahih Muslim Introduction 64, Introduction, Narration 63 : What is the significance of verifying the authenticity of narrators in Islamic tradition?

‘Indeed this one alleges he has met eighteen of the warriors of the battle of Badr’. Qatādah said: ‘This one was barely asking [about Ḥadīth] before the plague; he did not attend to anything from [seeking Ḥadīth] and he did not speak [to any scholars] regarding it. By Allah, al-Hasan did not narrate to us from a witness of the battle of Badr without an intermediary; and Sa’īd bin al-Musayyib did not narrate to us from a witness of the battle of Badr without an intermediary except from Sa’d bin Mālik’.