Narrated Abu Huraira: Allah's Apostle (pbuh) said, "When the month of Ramadan starts, the gates of the heaven are opened and the gates of Hell are closed and the devils are chained." (Sahih Bukhari - Volume 3, Book 31, Number 123)

Narrated Abu Huraira: Allah's Apostle (pbuh) said: "Whoever establishes prayers during the nights of Ramadan faithfully out of sincere faith and hoping to attain Allah's rewards (not for showing off), all his past sins will be forgiven." (Sahih Bukhari - Volume 1, Book 2, Number 36)

Narrated Abu Huraira: A Bedouin came to the Prophet and said, "Tell me of such a deed as will make me enter Paradise, if I do it." The Prophet (p.b.u.h) said, "Worship Allah, and worship none along with Him, offer the (five) prescribed compulsory prayers perfectly, pay the compulsory Zakat, and fast the month of Ramadan." The Bedouin said, "By Him, in Whose Hands my life is, I will not do more than this." When he (the Bedouin) left, the Prophet said, "Whoever likes to see a man of Paradise, then he may look at this man." (Sahih Bukhari - Volume 2, Book 23, Number 480)

Narrated Abu Huraira: The Prophet 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." (Sahih Bukhari, Volume 3, Book 31, Number 125)