Musnad Abu Ya'la al-Mawsili 150:314

'Amr ibn Muhammad narrated to us, Ya'qub ibn Ibrahim ibn Sa'd narrated to us, from his father, from Salih ibn Kaysan, from Ibn Shihab: Yahya ibn Sa'id ibn al-'As informed me that Sa'id ibn al-'As informed him that 'Uthman and 'Aishah narrated to him that Abu Bakr al-Siddiq asked for permission to enter upon the Messenger of Allah (may Allah bless him and grant him peace) while he was lying on his bed, wearing 'Aishah's garment. He gave permission to Abu Bakr while he was in that state. He said: So he fulfilled his need to him, then he departed. 'Uthman said: Then 'Umar asked for permission, and he gave him permission while he was in that state. So he fulfilled his need to him, then he departed. He said: 'Aishah said: "I did not see you show concern for Abu Bakr and 'Umar as you showed concern for 'Uthman." The Messenger of Allah (may Allah bless him and grant him peace) said: "Indeed, 'Uthman is a shy man. I feared that if I gave him permission while I was in that state, he would not convey his need."