The Book Pertaining to the Merits of the Companions (Allah Be Pleased With Them) of the Holy Prophet (May Peace Be Upon Him) (Kitab Al-Fada'il Al-Sahabah)
Muslim :: Book 31 : Hadith 5906
A'isha reported: Allah's Messenger (may peace be upon him) was lying in the bed in my apartment with his thigh or his shank uncovered that Abu Bakr sought permission to get in. It was given to him and he conversed in the same very state (the Prophet's thigh or shank uncovered). Then 'Umar sought permission for getting in and it was given to him and he conversed in that very state. Then 'Uthman sought permission for getting in; Allah's Messenger (may peace be upon him) sat down and he set right his clothes. Mubammad (one of the narrators) said: I do not say that it happened on the same day. He ('Uthman) then entered and conversed and as he went out, A'isha said: Abu Bakr entered aind you did not stir and did not observe much care (in arranging your clothes), then 'Umar entered and you did not stir and did not arrange your clothes, then 'Uthman entered and you got up and set your clothes right, thereupon he said: Should I not show modesty to one whom even the Angels show modesty.