Sahih Muslim Book 7, Hadith Number 3088.
Chapter : The wall of the Ka’ba and its door.
‘Aisha reported: I asked Allah’s Messenger (may peace be upon him) about Hijr, and the rest of the Hadith is the same. I also said: Why is it that the door has been made on a higher level, and one cannot (get into it) but with the help of a ladder? The rest of the Hadith is the same as reported above and the concluding words are: (I do not change it) out of the apprehension that their hearts may disapprove of it.”