When you are at the door of your brother, friend, associate or someone you wish to visit, knock at the door in a pleasant way which is sufficient to make your presence known. Do not unethically knock loudly or violently as a thug or an oppressor would do, thereby frightening its occupants.
A woman came to Imam Ahmad Ibn Hambal [Rahimahullah] seeking his opinion on a religious matter. She knocked at his door loudly. He came out saying, “This is the banging of Policeman!” (In other words, it is not befitting to knock in this manner).
Imam Bukhari [Rahimahullah] reported in his ‘Al-Adabul Al-Mufrad’ that the Sahabah [Radiallahu anhum] used to knock on the door of Rasulullah [Sallallahu álayhi wa sallam] with the tips of their nails (out of respect for him).
This soft and gentle knocking is appropriate when the inmates of the home are close to the door. As for those who are further away from the door, it is appropriate to knock on their door, or ring the bell loud enough to enable them to hear it, without banging. In this regard, the following hadith was mentioned earlier, “Gentleness adorns every act and its absence tarnishes it.”
In addition, Imam Muslim [Rahimahullah] reported that Rasulullah [Sallallahu álayhi wa sallam] also said, “Whoever is deprived of kindness is deprived of all good things.”
One should allow sufficient time between two knocks, to enable those making wudhu, performing Saláh or eating, to finish without rushing. Some ‘ulama have suggested that this interval be equal to the duration of fout rakaáts of saláh since it is possible that a person may have just commence the saláh before you knocked on the door.
If after three intervalled knocks, you feel that if the person you came to see was not busy, he would have answered you, then leave for Rasulullah [Sallallahu álayhi wa sallam] has said, “When any of you seeks permission thrice, and he is not granted permission, then he should leave.” [Sunan Abi Dawúd]
While waiting for permission, do not stand infront of the door. Rather, stand to the right or to the left.
When Rasulullah [Sallallahu álayhi wa sallam] would come to someone’s door, he would avoid facing the door directly. Instead, he would stand to the right or to the left of the entrance. [Sunan Abi Dawúd]