Narrated Sahl (Radi-Allahu 'anhu):

The Prophet (Sallallahu 'Alaihi Wa Sallam) 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