Musnad Ahmad 1153:692

Abu Kamil narrated to us, he said: Zuhayr narrated to us, he said: Abu Ishaq narrated to us, from al-Aswad, who said: Ibn al-Zubayr said to me: "Tell me some of what the Mother of the Believers used to confide in you, for there is many a thing she used to tell you that you would conceal from the people." He said: I said: "She told me a hadith, the beginning of which I have memorized. She said: The Messenger of Allah (peace and blessings of Allah be upon him) said: 'Were it not that your people are new to the Age of Ignorance'—or he said: 'to disbelief'—Ibn al-Zubayr said: 'I would have demolished the Kaaba and made for it two doors on the ground: a door through which people enter, and a door through which they exit.'" Abu Ishaq said: "And I saw it [the Kaaba] like that."