The Prophet (sallallaahu 'alaihi wasallam) said, "Whoever established prayers on the night of Qadr out of sincere faith and hoping for a reward from Allah, then all his previous sins will be forgiven; and whoever fasts in the month of Ramadan out of sincere faith, and hoping for a reward from Allah, then all his previous sins will be forgiven." [Bukhari Vol. 3 : No. 125]
The Prophet (sallallaahu 'alaihi wasallam) said, "There is a gate in Paradise called Ar-Raiyan, and those who observe fasts will enter through it on the Day of Resurrection and none except them will enter through it. It will be said, 'Where are those who used to observe fasts?' They will get up, and none except them will enter through it. After their entry the gate will be closed and nobody will enter through it." [Bukhari Vol. 3 : No. 120]
The Prophet (sallallaahu 'alaihi wasallam) said, "Whoever does not give up forged speech and evil actions, Allah is not in need of his leaving his food and drink (i.e. Allah will not accept his fasting.)" [Bukhari Vol. 3 : No. 127]
"Oh people! A great month is coming to you. A blessed month. A month in which there is one night that is better than a thousand months. A month in which Allah has made it compulsory upon you to fast by day, and voluntary to pray by night. Whoever draws nearer to Allah by performing any of the voluntary good deeds in this month shall receive the same reward as is there for performing an obligatory deed at any other time. And whoever discharges an obligatory deed in this month shall receive the reward of performing seventy obligations at any other time.
It is the month of Sabr (patience), and the reward for sabr is Heaven. It is the month of kindness and charity. It is a month in which a believer's sustenance is increased.
Whoever gives food to a fasting person to break his fast, shall have his sins forgiven, and he will be saved from the Fire of Hell, and he shall have the same reward as the fasting person, without the latter's reward being diminished at all." [Narrated by Ibn Khuzaymah]