Yahya bin Sa'id bin al-As narrates that Sayyiduna Sa'id bin al-As (may Allah be pleased with him) told him that Sayyiduna Abu Bakr (may Allah be pleased with him) asked the Messenger of Allah (peace and blessings be upon him) for permission to enter while he (peace and blessings be upon him) was lying on his bed, wearing the wrap of Sayyidah Aishah (may Allah be pleased with her). He (peace and blessings be upon him) gave Abu Bakr (may Allah be pleased with him) permission in that same state, so Abu Bakr (may Allah be pleased with him) attended to his need and then left. Then Sayyiduna Umar (may Allah be pleased with him) asked for permission in that same state, and he attended to his need and then left. Uthman (may Allah be pleased with him) said: Then I asked for permission, and the Messenger of Allah (peace and blessings be upon him) sat up and gathered his clothes about him. Then I attended to my need, then I left. Sayyidah Aishah (may Allah be pleased with her) said: "O Messenger of Allah, why were you not as careful for Abu Bakr and Umar as you were for Uthman?" He (peace and blessings be upon him) said: "Uthman is a modest man, and I feared that if I gave him permission in that state, he would not convey his matter to me."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5495