O you who have believed, do not enter the houses of the Prophet except when you are permitted for a meal, without awaiting its readiness. But when you are invited, then enter; and when you have eaten, disperse without seeking to remain for conversation. Indeed, that [behavior] was troubling the Prophet, and he is shy of [dismissing] you. But Allah is not shy of the truth.
And when you ask [his wives] for something, ask them from behind a partition. That is purer for your hearts and their hearts.
And it is not [conceivable or lawful] for you to harm the Messenger of Allah or to marry his wives after him, ever. Indeed, that would be in the sight of Allah an enormity.
Narrated `Umar: I said, "O Allah's Messenger (sallallaahu alayhi wa sallam)! Good and bad persons enter upon you, so I suggest that you order the mothers of the Believers (i.e. your wives) to observe veils." Then Allah revealed the Verses of Al- Hijaab.
[Sahih Al-Bukhaari Hadith No. 4790]
Narrated Anas: `Umar said, "I agreed with Allah in three things," or said, "My Lord agreed with me in three things.
I said, 'O Allah's Messenger (sallallaahu alayhi wa sallam)! Would that you took the station of Abraham as a place of prayer.'
I also said, 'O Allah's Messenger (sallallaahu alayhi wa sallam)! Good and bad persons visit you! Would that you ordered the Mothers of the believers to cover themselves with veils.' So the Divine Verses of Al-Hijab (i.e. veiling of the women) were revealed.
I came to know that the Prophet (sallallaahu alayhi wa sallam) had blamed some of his wives so I entered upon them and said, 'You should either stop (troubling the Prophet (sallallaahu alayhi wa sallam) ) or else Allah will give His Apostle better wives than you.' When I came to one of his wives, she said to me, 'O `Umar! Does Allah's Messenger (sallallaahu alayhi wa sallam) not have what he could advise his wives with, that you try to advise them?' " Thereupon Allah revealed:– "It may be, if he divorced you (all) his Lord will give him instead of you, wives better than you Muslims (who submit to Allah).." [Qur’aan 66.5]
[Sahih Al-Bukhaari Hadith No. 4483]