Musnad Abu Ya'la al-Mawsili 150:123

'Abd al-A'la narrated to us, Abu al-Ahwas narrated to us, from Ash'ath ibn Abi al-Sha'tha', from al-Aswad ibn Yazid, from 'A'ishah, who said: I asked about the wall: "Is it part of the House (the Ka'bah)?" He said: "Yes." I said: "Then why did they not include it in the House?" He said: "Your people's funds fell short." She said: "I said to him: 'What is the matter with its door being elevated?'" He said: "Your people did that so they could let in whoever they wished. And were it not that your people are recently removed from the Age of Ignorance, and I fear that their hearts would deny it, I would have considered including the Hijr in the House and placing its door level with the ground."