Riyad Us-Saliheen (Gardens of the Righteous)

Chapter 141
Seeking Permission to enter by telling one's Name

874. Anas (May Allah be pleased with him) reported in the course of his famous Hadith pertaining to Al-Isra' (the Ascension) that Messenger of Allah (PBUH) said, "Then Jibril (Gabriel) ascended along with me to the nearest heaven and requested for the gate to be opened. He was asked: `Who is there?' He replied: `Jibril.' He was asked: `Who is with you?' He said: `Muhammad.' Then he ascended to the second heaven and requested for the opening of the gate. He was asked: `Who is there?' He said: `Jibril.' He was asked: `Who is with you?' He replied: `Muhammad.' In the same way he ascended to the third, fourth and all the heavens (i.e., until the seventh). At all of the gates he was asked: `Who is there?' He replied: Jibril.'''
[Al-Bukhari and Muslim]

875. Abu Dharr (May Allah be pleased with him) reported: I stepped out one night and saw Messenger of Allah (PBUH) walking by himself. I began to walk in the moonlit night. He turned round and saw me and asked, "Who is there?'' I replied: "Abu Dharr.''
[Al-Bukhari and Muslim].

876. Umm Hani (May Allah be pleased with her) reported: I went to the Prophet (PBUH) who was taking a bath while Fatimah was screening him. He asked, "Who is there?'' I replied: "I am Umm Hani.''
[Al-Bukhari and Muslim].

877. Jabir (May Allah be pleased with him) reported: I went to the Prophet (PBUH) and knocked at the door (to seek permission). He asked, "Who is there?'' I said: "I''. He repeated, '' I, I?!'' as if he disliked it.
[Al-Bukhari and Muslim].

Commentary:  At the doorstep, the visitor should disclose his identity to the host. Secondly, to knock at the door or to ring the door-bell is tantamount to seeking permission to enter the house. When the host comes out, the visitor should first offer him As-Salam.