A. Yusuf Ali:Translation:
If you find no one 2981 in the house, enter not until
permission is given to you: if you are asked to go back,
go back: that makes for greater purity for yourselves:
and Allah knows well all that you do.

Muhammad Asad:Translation:
Hence, [even] if you find no one within [the house], do not enter it until you are given leave; 34 and if you are told, “Turn back,” then turn back. This will be most conducive to your purity; and God has full knowledge of all that you do.
2981 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.