Sahih Bukhari Volume 4, Book 54, Hadith Number 466.

Narated By ‘Abdullah bin Qais Al-Ashari : The Prophet said, “A tent (in Paradise) is like a hollow pearl which is thirty miles in height and on every corner of the tent the believer will have a family that cannot be seen by the others.” (Narrated Abu Imran in another narration, “(The tent is) sixty miles (in height.”)