(radi Allahu anhu) narrated that the Messenger of Allah (sal alaihi wa sallam) said: “Every deed of the son of Adam will be multiplied, a Hasanah will be multiplied to ten its like, up to seven hundred times. Allah, the Mighty and Sublime, said: ‘Except fasting. It is for Me and I shall reward for it. He gives up his desires and his food for my sake.’ The fasting person will have two moments of joy: Joy when he breaks his fast, and joy when he meets his Lord. And indeed the smell of his mouth is better to Allah than the fragrance of musk.” [The Book of Fasting: ]
The act of fasting is so beloved to Allah (subhana wa ta’ala) that the reward He has reserved for it is beyond telling. Normal good deeds are rewarded ten to seven hundred times, but Allah (subhana wa ta’ala) just leaves us to guess how much more it is that He will reward us for fasting for His sake!