Narrated Abu Huraira: Allah’s Apostle 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 :: Book# 31 :: Hadith# 123
Narrated Abu Huraira: The Prophet 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.)”
Sahih Bukhari :: Book# 31 :: Hadith# 127
Abu Huraira (may Allah be pleased with him) narrated that the Messenger of Allah (may peace he upon him) made a mention of the new moon and (in this connection) said: Observe fast when you see it (the new moon) and break fast when you see it (the new moon of Shawwal), but when (the actual position of the month is) concealed from you (on account of cloudy sky), then count thirty days.
(Muslim :: Book 6 Hadith 2381)
The thirst is gone, the veins are moistened and the reward is confirmed, if Allah wills
(Abu Dawud 2/306 and others)