THE HADITH ON FASTING
Abu Huraira related that the Prophet (peace and blessings be upon him) said: Whoever fasts during Ramadan with faith and seeking his reward from Allah will have his past sins forgiven. Whoever prays during the nights in Ramadan with faith and seeking his reward from Allah will have his past sins forgiven. And he who passes Lailat al-Qadr in prayer with faith and seeking his reward from Allah will have his past sins forgiven (Bukhari, Muslim).
Abu Huraira related that Rasulullah said: If anyone omits his fast even for one day in Ramadan without a concession or without being ill, then if he were to fast for the rest of his life he could not make up for it (Bukhari).
Abu Huraira related that the Prophet said: Allah the Majestic and Exalted said: "Every deed of man will receive ten to 700 times reward, except Siyam (fasting), for it is for Me and I shall reward it (as I like). There are two occasions of joy for one who fasts: one when he breaks the fast and the other when he will meet his Lord" (Muslim).
Abu Huraira related that Rasulullah said: Many people who fast get nothing from their fast except hunger and thirst, and many people who pray at night get nothing from it except wakefulness (Darimi).