Musnad Ahmad 1153:288

Ibn Numayr narrated to us, Hisham and Abu Usamah narrated to us, they said: Hisham informed us—the meaning is the same—from his father, from Aisha, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Were it not for the recentness of your people's era in disbelief, I would have demolished the Kaaba, then I would have rebuilt it upon the foundation of Ibrahim (peace be upon him), for when the Quraish built it, they shortened it. And I would have made a back entrance for it." Abu Usamah said: "A back entrance."