The number of levels (stages) in Heaven is (equivalent to) the number of verses in the Qur'an (6236). Thus, when a reciter of the Qur'an enters into Heaven, it will be said to him: 'Go up one level for every verse that you can recite.' Thus, no one will be in a higher level than the one who has memorized the entire Qur'an.

Biharul Anwar, Volume 92, Page 22 - Shi'ite Hadith