What were the Tabi'un who narrated from the Companions doing before Ibn Sirin and Shu'bah to ascertain the uprightness and precision of narrators, especially given that Malik abandoned those entrusted with the treasury but who were not strong in hadith? And were Ibn Sirin or Shu'bah the only ones who investigated and critiqued in their time, and is it sufficient for one or two men to do this?

The verification of narrations originated during the time of the Companions. The need for isnad (chain of narration) and discussion about narrators arose to authenticate and verify narrations, especially after the emergence of people of innovation who fabricated hadiths to strengthen their doctrines. This need became particularly acute during the era of the Tabi'in (successors). Ibn Sirin used to say, "They did not inquire about the isnad, but when the tribulation occurred, they said: 'Name your narrators for us.' Then they would look at the people of Sunnah and accept their hadith, and at the people of innovation and not accept their hadith." It became widely known that Shu'bah was the first to extensively engage in al-Jarh wa al-Ta'dil (discrediting and accrediting narrators), discussing the continuity and discontinuity of isnads, and delving into the intricacies of the science of 'ilal (hidden defects). Al-Tirmidhi mentioned that imams from among the Tabi'in spoke about narrators before Shu'bah, such as Al-Hasan Al-Basri, Tawus, Sa'id ibn Jubayr, and others. This was done as advice to Muslims and to clarify the status of narrators, including the weak, the innovators, and those accused (of lying), because testimony in matters of religion is more deserving of verification than testimony in matters of rights and property.