Musnad Abu Ya'la al-Mawsili 149:81

'Abd al-A'la narrated to us, 'Uthman ibn 'Umar narrated to us, Ibn Abi Dhi'b narrated to us, from al-Zuhri, from Yahya ibn Sa'id ibn al-'As, from his father, from 'A'ishah, who said: Abu Bakr came seeking permission to enter upon the Messenger of Allah (may Allah bless him and grant him peace), while he was wearing the wrap of the Mother of the Believers. He gave him permission, and he fulfilled his need with him, then he left. Then 'Umar sought permission to enter upon him, and he gave him permission while he was in that same state. He fulfilled his need with him, then he left. Then 'Uthman sought permission to enter, and the Messenger of Allah (may Allah bless him and grant him peace) sat up straight and said to 'A'ishah: "Gather your clothes upon yourself." Then he gave him permission. When he left, 'A'ishah said to him: "Why did you not become concerned for Abu Bakr and 'Umar as you became concerned for 'Uthman?" He said: "Indeed, 'Uthman is a shy man, and if I had given him permission while in that state, I feared that he would not convey his need."