Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) said: "Abu Bakr al-Siddiq: you have hit upon his name correctly. Umar was a horn of iron. Uthman Dhu al-Nurayn: you have hit upon his name correctly; he was killed wrongfully, and he was given a double reward for it."
Hadith Referenceالمعجم الكبير للطبراني / العشرة / 138