Musnad Abu Ya'la al-Mawsili 154:133

Muhammad ibn Yahya narrated to us, he said: Muhammad ibn al-Harith narrated to us, Muhammad ibn Abd al-Rahman informed us, from his father, from Ibn Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The most compassionate of my Ummah toward my Ummah is Abu Bakr, and the most severe of them regarding the religion of Allah is Umar, and the most truthful of them in modesty is Uthman ibn Affan, and the best of them in judgment is Ali ibn Abi Talib, and the most knowledgeable of them in the laws of inheritance is Zayd ibn Thabit, and the most knowledgeable of them in the lawful and the unlawful is Muadh ibn Jabal, and the best of them in recitation is Ubayy ibn Ka'b. And every nation has a trustee, and the trustee of this nation is Abu Ubaydah ibn al-Jarrah."