The month of Ramadan is the one in which the Quran was sent down, a guidance for mankind, clear proofs for the guidance, the Criterion; so whoever amongst you witnesses this month, let him fast it. (Surah al-Baqarah 2:185)

Ramadan, a blessed month, has come to you during which Allah has made it obligatory for you to fast. In it the gates of Heaven are opened, the gates of al-Jahim are locked, and the rebellious devils are chained. In it Allah has a night which is better than a thousand months. He who is deprived of its good has indeed suffered deprivation. (Hadith - Al-Tirmidhi, Narrated Abu Hurayrah)

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. (Hadith - Sahih Bukhari, Narrated Abu Hurayrah)