Shama-il Tirmidhi Chapter 048, Hadith Number 002 (342).

'Aayeshah Radiyallahu 'Anha reports: (because of the excessive modesty of Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam) "I did not have the courage to see the private parts of Rasulullah Sallallahu'Alayhi Wasallam, or that I never saw the private parts of Rasulullah Sallallahu 'Alayhi Wasallam".

Commentary
Due to the shame-fastness of Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam this was not possible, then how could Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam himself have done so? It is natural that in the presence of a modest person, one is compelled to act modestly. In another narration it is clearly denied that never did Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam see my private parts, nor did I see the private parts of Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam. Although 'Aayeshah Radiyallahu 'Anha was the most informal among all the wives, she was also the most beloved. If this was his manner with her, what can be said of the others? Sayyiditina Ummi Salamah Radiyallahu 'Anha says that when Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam slept with his wife, he closed his eyes and bowed down his head, and also stressed to his wife to be calm and dignified. Ibn 'Abbaas Radiyallahu 'Anhu narrates that Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam went behind the rooms to perform ghusl. Nobody saw the private parts of Sayyidina Rasulullah Sallallahu'Alayhi Wasallam. Before the advent of nubuwwah, when the Ka'bah was rebuilt Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam also carried stones and brought them. According to 'Arab custom, no importance was given to concealing the private parts. Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam (happen to) put his lungi under the stone, and immediately became unconscious (due to modesty) and fell down, whereas, at that time the shar'ee injunctions were not even revealed.