Seeking Permission and the Etiquette of entering Houses

This is the Islamic etiquette. Allah taught these manners (of seeking permission) to His believing servants and commanded them not to enter houses other than their own until they had asked permission, i.e., to ask for permission before entering and to give the greeting of Salam after asking. One should seek permission three times, and if permission is given, (he may enter), otherwise he should go away.It was reported in the Sahih that when Abu Musa asked `Umar three times for permission to enter and he did not give him permission, he went away. Then `Umar said, "Did I not hear the voice of `Abdullah bin Qays asking for permission to enter Let him come in." So they looked for him, but found that he had gone. When he came later on, `Umar said, "Why did you go away" He said, "I asked for permission to enter three times, but permission was not given to me, and I heard the Prophet say,

«إِذَا اسْتَأْذَنَ أَحَدُكُمْ ثَلَاثًا فَلَمْ يُؤْذَنْ لَهُ فَلْيَنْصَرِفْ»

لَّيْسَ عَلَيْكُمْ جُنَاحٌ أَن تَدْخُلُوا بُيُوتًا غَيْرَ‌ مَسْكُونَةٍ فِيهَا مَتَاعٌ لَّكُمْ

There is no sin on you if you enter uninhabited houses in which you have rightful benefit - 24:29.