Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1745
'A'isha reported Allah's Messenger (may peace be upon him) (as saying): One who is proficient in the Qur'an is associated with the noble, upright, recording angels; and he who falters in it, and finds it difficult for him, will have a double reward.