Musnad Ahmad 1153:1321

'Abd al-Razzaq narrated to us, he said: Ma'mar informed us, from al-Zuhri, from Yahya ibn Sa'id ibn al-'As, from 'Aishah, she said: Abu Bakr sought permission to enter upon the Messenger of Allah, peace and blessings of Allah be upon him, while I was with him under a single garment. She said: So he gave him permission, and he fulfilled his need with him while he was with me under the garment, then he left. Then 'Umar sought permission to enter upon him, so he gave him permission, and he fulfilled his need with him in that state, then he left. Then 'Uthman sought permission to enter upon him, so he adjusted his clothes upon himself and sat up, and he fulfilled his need with him, then he left. 'Aishah said: So I said to him: "O Messenger of Allah, Abu Bakr sought permission to enter upon you, and he fulfilled his need with you in that state of yours; then 'Umar sought permission to enter upon you, and he fulfilled his need with you in that state; then 'Uthman sought permission to enter upon you, and it was as if you were cautious?" He said: "Indeed, 'Uthman is a shy man, and if I had given him permission in that state, I feared that he would not fulfill his need with me."