كتاب الحج
15  
The Book of Pilgrimage
(70)
Chapter: The wall and the door of the Ka'bah
(70)
باب جَدْرِ الْكَعْبَةِ وَبَابِهَا ‏‏
Sahih Muslim 1333 j

'A'isha (Allah be pleased with her) reported:

I asked Allah's Messenger (ﷺ) about the wall, circumpassing the House (i. e. whether the wall on the side of Hijr was included in the Ka'ba). He said, Yes. I said: Then why did they not include it in the House? He said: 'Your people ran short of the means (to do so). I said: Why is it that the level of its door is raised high? He said: Your people did it so that they should admit one whom they liked, and forbid him whom they disliked, and if your people were not new converts to faith, and I did not apprehend that their hearts would feel agitated at this. I would have definitely included (the area of) this wall-in the House and would have brought the door to the level of the ground.
حَدَّثَنَا سَعِيدُ بْنُ مَنْصُورٍ، حَدَّثَنَا أَبُو الأَحْوَصِ، حَدَّثَنَا أَشْعَثُ بْنُ أَبِي الشَّعْثَاءِ، عَنِ الأَسْوَدِ بْنِ يَزِيدَ، عَنْ عَائِشَةَ، قَالَتْ سَأَلْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم عَنِ الْجَدْرِ أَمِنَ الْبَيْتِ هُوَ قَالَ ‏"‏ نَعَمْ ‏"‏ ‏.‏ قُلْتُ فَلِمَ لَمْ يُدْخِلُوهُ فِي الْبَيْتِ قَالَ ‏"‏ إِنَّ قَوْمَكِ قَصَّرَتْ بِهِمُ النَّفَقَةُ ‏"‏ ‏.‏ قُلْتُ فَمَا شَأْنُ بَابِهِ مُرْتَفِعًا قَالَ ‏"‏ فَعَلَ ذَلِكِ قَوْمُكِ لِيُدْخِلُوا مَنْ شَاءُوا وَيَمْنَعُوا مَنْ شَاءُوا وَلَوْلاَ أَنَّ قَوْمَكِ حَدِيثٌ عَهْدُهُمْ فِي الْجَاهِلِيَّةِ فَأَخَافَ أَنْ تُنْكِرَ قُلُوبُهُمْ لَنَظَرْتُ أَنْ أُدْخِلَ الْجَدْرَ فِي الْبَيْتِ وَأَنْ أُلْزِقَ بَابَهُ بِالأَرْضِ ‏"‏ ‏.‏
Reference : Sahih Muslim 1333j
In-book reference : Book 15, Hadith 453
USC-MSA web (English) reference : Book 7, Hadith 3087
  (deprecated numbering scheme)