Surah 24. An-Nur, Ayah 28

I.e., by the rightful owner or caretaker.

That is, if no one replies; there may be people in the house not in a presentable state. Or, even if the house is empty, you have no right to enter it until you obtain the owner's permission, wherever he may be. The fact of your not receiving a reply does not entitle you to enter without permission. You should wait, or knock twice or three times, and withdraw in case no permission is received. If you are actually asked to withdraw, as the inmates are not in a condition to receive you, you should a fortiori withdraw, either for a time, or altogether, as the inmates may wish you to do. Even if they are your friends, you have no right to take them by surprise or enter against their wishes. Your own purity of life and conduct as well as of motives is thus tested.