Sahih Bukhari
Prophetic Commentary on the Quran (Tafseer of the Prophet (PBUH))
Volume: 006 / Book Number: 060 / Hadith Number: 459
Narrated Aisha:
The Prophet said, "Such a person as recites the Quran and masters it by heart, will be with the noble righteous scribes (in Heaven). And such a person exerts himself to learn the Quran by heart, and recites it with great difficulty, will have a double reward."