Musnad Abu Ya'la al-Mawsili 150:311

Yahya ibn Ayyub narrated to us, Ismail ibn Ja'far narrated to us, Muhammad ibn Abi Harmalah informed me, from 'Ata' and Sulayman, the sons of Yasar, and Abu Salamah ibn 'Abd al-Rahman, that 'Aisha said: The Messenger of Allah (may Allah bless him and grant him peace) was lying down in his house, with his thighs or his shins uncovered. Abu Bakr asked for permission [to enter], so he gave him permission while he was in that state, and he spoke. Then 'Umar asked for permission, so he gave him permission while he was like that, and he spoke. Then 'Uthman asked for permission, so the Messenger of Allah (may Allah bless him and grant him peace) sat up and adjusted his clothes. Muhammad [ibn Abi Harmalah] said: I do not say that this was on one day. So he entered and spoke. When he left, 'Aisha said: "O Messenger of Allah, Abu Bakr entered and you did not sit up nor pay him any mind. Then 'Umar entered and you did not show excitement for him nor pay him any mind. Then 'Uthman entered and you sat up and adjusted your clothes?" He said: "Should I not be shy of a man whom the angels are shy of?"