Abu Ayyub (R.A) reported: The Messenger of Allah said, " He who observes As-Saum (the fasting) in the month of Ramadan, and also observes As-Saum for six days in the month of Shawwal, it is as if he has observed As-Saum for the whole year."
The Prophet (peace be upon him), “Should I not inform you of that which I fear for you even more than the dangers of dajjaal? It is the hidden shirk: A person stands to pray and he beautifies his prayer because he sees the people looking at him”.
(Sahih; Sunan ibn Majah)
Abu Hurairah (radi Allahu anhu) narrated that the Messenger of Allah (sal Allahu alaihi wa sallam) said: ‘When Ramadhan comes, the gates of mercy are opened and the gates of Hell are shut, and the devils are put in chains.
[The Book of Fasting: Sahih Muslim]