Sunan Ibn Majah 154
It was narrated from Anas bin Malik that:
The Messenger of Allah said: The most merciful of my Ummah towards my Ummah  is Abu Bakr; the one who adheres most sternly to the religion of Allah is 'Umar; the most sincere of them in shyness and modesty is 'Uthman; the best judge is 'Ali bin Abu Talib; the best in reciting the Book of Allah is Ubayy bin Ka'b; the most knowledgeable of what is lawful and unlawful is Mu'adh bin Jabal; and the most knowledgeable of the rules of inheritance (Fara'id) is Zaid bin Thabit. And every nation has a trustworthy guardian, and the trustworthy guardian of this Ummah is Abu 'Ubaidah bin Jarrah."
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا عَبْدُ الْوَهَّابِ بْنُ عَبْدِ الْمَجِيدِ، حَدَّثَنَا خَالِدٌ الْحَذَّاءُ، عَنْ أَبِي قِلاَبَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ قَالَ ‏
"‏ أَرْحَمُ أُمَّتِي بِأُمَّتِي أَبُو بَكْرٍ وَأَشَدُّهُمْ فِي دِينِ اللَّهِ عُمَرُ وَأَصْدَقُهُمْ حَيَاءً عُثْمَانُ وَأَقْضَاهُمْ عَلِيُّ بْنُ أَبِي طَالِبٍ وَأَقْرَؤُهُمْ لِكِتَابِ اللَّهِ أُبَىُّ بْنُ كَعْبٍ وَأَعْلَمُهُمْ بِالْحَلاَلِ وَالْحَرَامِ مُعَاذُ بْنُ جَبَلٍ وَأَفْرَضُهُمْ زَيْدُ بْنُ ثَابِتٍ أَلاَ وَإِنَّ لِكُلِّ أُمَّةٍ أَمِينًا وَأَمِينُ هَذِهِ الأُمَّةِ أَبُو عُبَيْدَةَ بْنُ الْجَرَّاحِ ‏"‏ ‏.‏