An-Nur · 24:27

27. O those who have faith in Allah and act on His sacred law, do not enter houses besides your own houses until you seek permission from their inhabitants to enter them and you greet them, by saying in greeting and seeking permission: “Peace be on you, can I come in?” That seeking permission you have been ordered is better for you than entering suddenly, so that you remember what you have been ordered and then carry it out.