"The Prophet performed Salat in the interior of the Ka'bah." And Ibn Abbas said: "He did not perform Salat in it, but he said the Takbir."
Jami` at-Tirmidhi Book 9, Hadith 67
← Previous Hadith "The Prophet left me while he had a joyous look of contentment and he returned to me grieving. So I asked him about that and he said: 'I entered the Ka'bah, and I wished that I had not done it. I fear that my Ummah will follow me (in that) after me.'"

Jami` at-Tirmidhi Book 9, Hadith 66 Next Hadith → Ibn Az-Zubair said to him: "Narrated to me from what the Mother of the Believers used to (secretly) inform you about" - meaning Aishah - so he said: "She narrated to me that the Messenger of Allah said: 'Had your people not been still close to the pre-Islamic period of ignorance, then I would demolish the Ka'bah and rebuild it with two doors.'" He said: "So when Ibn Az-Zubair came to power he demolished it and rebuilt it with two doors."

Jami` at-Tirmidhi Book 9, Hadith 68