He was conspicuous for his modesty. According to the Holy Prophet, after the prophets, Uthman was most conspicuous for his modesty. We have it on the authority of Ayesha that when the Companions like Abu Bakr and Umar visited the Holy Prophet, the Holy Prophet would receive them without any formality, but when Uthman visited him he took care to be very formal
That was because of the modesty of Uthman. The Holy Prophet said that unless he paid due regard to Uthman, a modest person like him was not likely to say what he wanted to say. The Holy Prophet also used to say that the angels of God stood abashed before Uthman as they stood abashed before the Prophets.