Al-Isaabah fi Tamyeez Al-Sahaabah is a comprehensive work by Ibn Hajar al-Asqalani that focuses on detailing the biographies of the companions of the Prophet Muhammad. The book is respected for its depth and scope, covering over 12,000 biographies of companions and setting criteria for distinguishing between sound companions and others. Ibn Hajar spent forty years completing this monumental work, which spans from the pre-Islamic era to the death of the last recognized companion.