Musnad Ahmad 543
Al-Hasan mentioned `Uthman`s extreme shyness and said:
If he was in a room with the door closed, and he took off his garment to pour water on himself, shyness prevented him from standing up straight.
حَدَّثَنَا عَبْدُ الصَّمَدِ، حَدَّثَنَا سَالِمٌ أَبُو جُمَيْعٍ، حَدَّثَنَا الْحَسَنُ، وَذَكَرَ، عُثْمَانَ رَضِيَ اللَّهُ عَنْهُ وَشِدَّةَ حَيَائِهِ فَقَالَ إِنْ كَانَ لَيَكُونُ فِي الْبَيْتِ وَالْبَابُ عَلَيْهِ مُغْلَقٌ فَمَا يَضَعُ عَنْهُ الثَّوْبَ لِيُفِيضَ عَلَيْهِ الْمَاءَ يَمْنَعُهُ الْحَيَاءُ أَنْ يُقِيمَ صُلْبَهُ‏.‏