According to a hadith, a person will be rewarded from ten fold to 700 fold for his good deeds. Every good deed that a person does, God rewards him ten fold. But if the deed is performed with heightened spiritual feelings, he would be rewarded 700 fold. 
     God says: "Except for fasting. Because it is for Me and I will give the reward for it." (Sahih Muslim 1151) If you reflect, you will see that the Lord of the universe is saying: 'Fasting is for Me. I will give its reward.' God will indeed give abundant reward. There is no measure for it. He will give limitless reward. For other deeds, the reward is measurable -- ten fold, 200 fold or 700 fold. But it is said that if a person observes fasting sincerely, he will be rewarded for it immeasurably, without any limit. There cannot be any greater good tiding than this. But this is true only for a person who observes fasting in its true spirit. That is, a person should fast for a month but it must have its effects throughout his life. That is true fasting. If you observe fasting as a ritual without understanding the wisdom and spirit behind it, then there will be no reward.