For Full Lecture :
"Islam Mein Parday Kay Ehkaam - Dr. Israr Ahmed"

A home is a place where one finds peace. Allah Ta'ala Himself declares in the Holy Qur'aan that He has created homes for us to acquire peace and comfort. One can only enjoy this peace and comfort if one is safe from unnecessary interferences and disturbances. Islaam has taught us a very important etiquette in this regard which is called Isti'zaan (to seek permission before entering a home). Allah Ta'ala says in the Holy Qur'aan:
O! You who Believe Let your slaves and your children first ask your permission (before they come to you in your privacy) on three occasions: before the Fajar Salaah; while you remove your extra clothing for the mid day heat; and after the Esha Salaah.

Wisdom of seeking permission :

Seeking permission eliminates the possibility of obscenity and immorality. If one enters someone's home without seeking permission, it is possible that one may see the women of the house which may lead to haraam or forbidden situations. Furthermore, one may be engaged in intimate or personal activities which require privacy. If someone enters unannounced, one will be deprived of privacy.

The following are some important rules regarding Isti'zaan (seeking permission)

Rule No. 1
It is Fardh (obligatory) on every person to practice Isti'zaan i.e. to seek permission to enter someone's house). This applicable even when a male visits a male or a female visits a female and they are mahram. Therefore, even if a person visits his own mother, sister, or any other mahram woman, he should first seek permission before entering her house or room. Imaam Maalik (RA) has narrated in his Mu'atta, that someone asked Rasulullah (Sallallahu Alayhi Wasallam) whether he should seek permission before going to meet his mother. Rasulullah (Sallallahu Alayhi Wasallam) said, "Yes, do seek her permission." That person asked, "But I am living in the same house with my mother." Rasulullah (Sallallahu Alayhi Wasallam) said, "Even then, you should not enter the house without taking her permission." Again this person asked, "O messenger of Allah (Sallallahu Alayhi Wasallam), I am always at her service." He (Sallallahu Alayhi Wasallam) replied, "You should still ask her permission. Would you like to see your mother naked?" He replied, "No, No". Thereafter Rasulullah (Sallallahu Alayhi Wasallam) said, "Therefore you should first seek permission because there is a possibility that she may have uncovered some part of herself due to some need. (Mazhari Vol. 6 Pg.488).

Rule No. 2
If someone is living alone in his home with his wife, even then it is preferable and a Sunnah to make some sort of sound before entering to make it known that he is arriving. However this is not obligatory. The wife of Hadhrat Abdullah Ibn Mas'ood (Radi Allahu Anhu) has reported that whenever he came into the house he would always make a humming sound to announce his arrival so that he would not see the house people in a condition that he would not like.

Rule No. 3
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Rule No. 4
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Rule No. 5
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Rule No. 6
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Rule No. 7
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Rule No. 8
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Conclusion
Islaam has taught us the details of social etiquette. Ibn Abbaas (Radi Allahu Anhu) used to say that there are three verses which people have stopped practising upon and one of them is the verse of Isti'zaan (seeking permission to enter someone's house). He has also mentioned that shaytaan has overpowered people in respect to these three verses. He has stated that he did not even allow his slave girl to come to him without taking permission at these three times.

May Allah Ta'ala grant us all taufeeq. Aameen

Ref : http://talimiboardkzn.org/?q=node/186