On the authority of Abu Hurayrah (may Allah be pleased with him) from the Prophet (peace and blessings of Allah be upon him), who said:

"Allah (mighty and sublime be He) says:

'Fasting is Mine and it is I Who give reward for it. [A man] gives up his sexual passion, his food and his drink for My sake.' Fasting is like a shield, and he who fasts has two joys: a joy when he breaks his fast and a joy when he meets his Lord. The change in the breath of the mouth of him who fasts is better in Allah's estimation than the smell of musk."

[Bukhari (also by Muslim, Malik, at-Tirmidhi, an-Nasa'i and Ibn Majah).]