From Sahih Bukhari (Hadith 4937):
Narrated Aisha:The Prophet (ﷺ) said, "Such a person as recites the Qur'an and masters it by heart, will be with the noble righteous scribes (in Heaven). And such a person exerts himself to learn the Qur'an by heart, and recites it with great difficulty, will have a double reward
Reference: Bukhari 4937