Sahih Bukhari Volume 6, Book 61, Hadith Number 513.

Narrated By ‘Abdullah bin ‘Abbas : Allah’s Apostle said, “Gabriel recited the Qur’an to me in one way. Then I requested him (to read it in another way), and continued asking him to recite it in other ways, and he recited it in several ways till he ultimately recited it in seven different ways.”