Narrated Abdullah:
The Prophet said, "It is a bad thing that some of you say, 'I have forgotten such-and-such verse of the Qur'an,' for indeed, he has been caused (by Allah) to forget it. So you must keep on reciting...
None has the right to be worshipped but Allah alone, Who has no partner. His is the dominion and His is the praise and He is Able to do all things. (Recite 100 times in Arabic upon rising in the morning).
Info: Whoever recites this one hundred times a day will have the reward of freeing ten slaves. One hundred Hasanaat (rewards) will be written for him and one hundred misdeeds will be washed away. He will be shielded from Satan until the evening. No one will be able to present anything better than this except for someone who has recited more than this. Al-Bukhari 4/95, Muslim 4/2071.