Etiquette of asking permission

O you who believe, do not enter other houses except yours without first asking permission and saluting the inmates. This is better for you: You may haply take heed.

If you find that no one is in, then do not enter unless you have received permission. If you are asked to go away, turn back. That is proper for you. God is aware of what you do.

There is no harm in going into uninhabited houses where there is some convenience for you, as God has knowledge of what you hide and what you disclose.