Biographical evaluation (ʿilm al-rijāl; literally meaning 'Knowledge of Men' , but more commonly understood as the Science of Narrators) refers to a discipline of Islamic religious studies within hadith terminology in which the narrators of hadith are evaluated. Its goal is to establish the credibility of the narrators, using both historic and religious knowledge, in order to distinguish authentic and reliable hadiths from unreliable hadiths. is synonymous with what is commonly referred to as (discrediting and accrediting) – the criticism and declared acceptance of hadith narrators.
In his Introduction to the Science of Hadith, Ibn al-Salah, a renowned hadith specialist, explained the importance of the study of hadith narrators. Introducing the chapter entitled, 'Recognizing the trustworthy, reliable narrators and those who are weak and unreliable,' Ibn al-Salah said, "This is from the most distinguished and noble types (of hadith study) as it results in recognizing the authenticity of a hadith or its weakness." He then explained that any criticism directed at a narrator was permissible due to the "maintenance of the Shariah, purging it of any mistakes or misinformation".
Stressing the importance of biographical evaluation, Ali ibn al-Madini, an early authority on the subject, said, "Knowing the narrators is half of knowledge."
While many Companions narrated hadith, according to Ahmad ibn Hanbal there were six who were the most prolific narrators of them, who lived long lives enabling them narrate to a large extent. They were: Abu Huraira, Abdullah ibn Umar, Aisha, Jabir ibn Abdullah, Ibn Abbas and Anas ibn Malik with Abu Huraira being the most prolific of them. According to Ibn al-Salah the most prolific narrators from the Companions was Abu Huraira followed by Ibn Abbas.
In spite of the Companions' efforts in narrating their hadith, there was no need for them to evaluate each other's narrating capabilities or trustworthiness.