The Prophet of Allah, sallallaahu ‘alayhi wa sallam, praised them for their unique characteristics:

“The most merciful of my Nation with my Nation is Abu Bakr; the strongest [in adhering to] Allah’s Religion is `Umar; the one with the most shyness is `Uthmaan; the best judge is `Ali ibn Abu Talib; the most knowledgeable of the Quran is Ubayy ibn Ka'b; the most knowledgeable with regard to lawful and unlawful matters is Mu'adh ibn Jabal; the most knowledgeable with regard to inheritance is Zayd ibn Thaabit. Every nation has a custodian, and the custodian of this Nation is Abu `Ubaidah ibn Al-Jaarrah