Ibn 'Abbas, may Allah be pleased
with them, narrated:

Allah's Messenger (may peace be upon him)
transmitted it from the Blessed and Great Lord: Verily Allah recorded the good
and the evil and then made it clear that he who intended good but did not do it,
Allah recorded one complete virtue in his favor, but if he intended it and also
did it, the Glorious and Great Allah recorded ten to seven hundred virtues and
even more to his credit. But if he intended evil but did not commit it, Allah
wrote down one full virtue in his favor. If he intended that and also committed
it, Allah made an entry of one evil against him.

Hadith
number in Sahih Muslim [Arabic only]: 187