Al-Isabah fi Tamyiz as-Sahabah

الإصابة في تمييز الصحابة

The most comprehensive biographical dictionary of the Companions of the Prophet, covering over 12,000 entries. Ibn Hajar verified each person's status as a Companion using strict hadith methodology, distinguishing between confirmed Companions, those whose companionship is disputed, and those mistakenly listed in earlier works. It is the definitive reference for identifying and authenticating the Companions.