Every act of goodness is rewarded. Rewards are given based on the sincerity of the intention. Fasting is the only worship about which Allah has said that He Himself is the reward for it. This means that one develops such a close relationship with Allah that Allah Himself becomes the helper.
Abu Hurairah relates that the Holy Prophet, peace be upon him, said: "Allah, the Lord of Honor and glory says: All other deeds of man are for himself, but his fasting is purely for Me and I shall reward him for it. The fast is a shield. When any of you is fasting he should abstain from loose talk and noisy exchanges. Should anyone revile him or seek to pick a quarrel with him, he should respond with: I am observing a fast. By Him in Whose hands is the life of Muhammad, the breath of one who is fasting is purer in the sight of Allah than the fragrance of musk. One who fasts experiences two joys: he is joyful when he breaks his fast, and he is joyful by virtue of his fast when he meets his Lord" (Bukhari and Muslim).
Sa'ad ibn Sahl relates that the Holy Prophet, peace be upon him, said: "There is a gate of Paradise called Rayyan through which only those will enter on the Day of Judgment who are regular in observing the fast and no one else. A call will go forth: Where are those who observed the fast regularly? And they will step forth and no one beside them will enter through that gate. After they shall have entered, the gate will be closed and no one else will enter thereby" (Bokhari and Muslim).
Abu Sa'id Khudri relates that the Holy Prophet, peace be upon him, said: "When a servant of Allah observes the fast for a day for the sake of Allah, He thereby repels the Fire from him a distance of seventy years of journeying" (Bokhari and Muslim).
Abu Hurairah relates that the Holy Prophet, peace be upon him, said: "He who observes the fast during Ramadan out of sincerity of faith and in hope of earning merit will have his past sins forgiven him" (Bokhari and Muslim).
Abu Hurairah relates that the Holy Prophet, peace be upon him, said: "When Ramadan arrives the gates of Paradise are opened and the gates of hell are locked up and satans are put in chains" (Bokhari and Muslim).