Sunan At-Tirmidhi

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