On the making it clear that the Sunna is that when the one from whom one asks permission to enter says, "Who is it?"

Riyad as-Salihin (The Meadows of the Righteous)

by Imam Nawawi

141. Chapter: On the making it clear that the Sunna is that when the one from whom one asks permission to enter says, "Who is it?" he should name himself in the manner by which he is known by and not say "I"

874. Anas said in his famous hadith about the Night Journey that the Messenger of Allah, may Allah bless him and grant him peace, said, "Then Jibril took me up to the nearest heaven and asked for it to be opened. It was said, 'Who is this?' He said, 'This is Jibril.' It was said, 'Who is with you?' He said, 'Muhammad.' Then he went to the second, third, fourth and the rest of the heavens and it was said at the gate of every heaven, 'Who is this?' and he replied, 'Jibril." [Agreed upon]

875. Abu Dharr said, "I went out one night and there was the Messenger of Allah, may Allah bless him and grant him peace, walking alone. I began to walk in the shadow out of the moonlight but he turned and saw me and said, 'Who is that?' I answered, 'Abu Dharr.'" [Agreed upon]

876. Umm Hani' said, "I went to the Prophet, may Allah bless him and grant him peace, and found him washing with Fatima screening him. He asked, 'Who is it?' I replied, 'It is Umm Hani.'" [Agreed upon]

877. Jabir said, "I came to the Prophet, may Allah bless him and grant him peace, and knocked at the door. He said, 'Who is it?' I said, 'I.' He said, 'I, I?' as if he disliked it." [Agreed upon]