Narrated Bahz bin Hakim:
My father narrated to me from my grandfather, who said: 'I said: O Messenger of Allah! Regarding our 'Awrah, what of it must we cover and what of it may we leave? He said: Protect your 'Awrah except from your wife or what your right hand possesses. ' He said: What about a man with another man? He said: If you are able to not let anyone see it, then do so. I said: What about a man when he is alone? He said: Allah is most deserving of being shy from Him.