Sahih Bukhari | Volume 5 | Hadith Number 171

Narrated by 'Amr bin Dinar and 'Ubaidullah bin Abi Yazid
In the lifetime of the Prophet there was no wall around the Ka'ba and the people used to pray around the Ka'ba till 'Umar became the Caliph and he built the wall around it. 'Ubaidullah further said, "Its wall was low, so Ibn Az-Zubair built it."