The obligation of the fast of Ramadhaan and it's time

Fasting in Islam is one of its great (important) pillars, without which one's religion is incomplete.

Al-Baqarah (183 - 185)

183. O ye who believe! Fasting is prescribed to you as it was prescribed to those before you, that ye may (learn) self-restraint,

184. (Fasting) for a fixed number of days; but if any of you is ill, or on a journey, the prescribed number (Should be made up) from days later. For those who can do it (With hardship), is a ransom, the feeding of one that is indigent. But he that will give more, of his own free will,- it is better for him. And it is better for you that ye fast, if ye only knew.

185. Ramadhan is the (month) in which was sent down the Qur'an, as a guide to mankind, also clear (Signs) for guidance and judgment (Between right and wrong). So every one of you who is present (at his home) during that month should spend it in fasting, but if any one is ill, or on a journey, the prescribed period (Should be made up) by days later. Allah intends every facility for you; He does not want to put to difficulties. (He wants you) to complete the prescribed period, and to glorify Him in that He has guided you; and perchance ye shall be grateful.

The Prophet (sal-Allaahu `alayhe wa sallam) said:

((Whoever fasts during the month of Ramadhaan, out of sincere faith and hoping to attain Allaah's rewards, then all his previous sins will be forgiven)).

The Prophet (sal-Allaahu `alayhe wa sallam) also said:

((When the month of Ramadhaan starts, the gates of the Heaven are opened and the gates of Hell are closed and the devils are chained)).

The Prophet (sal-Allaahu `alayhe wa sallam) also said:

((Fasting is a shield or protection from the fire and from committing sins. If one of you is fasting, he should avoid sexual relation with his wife and quarrelling, and if somebody should fight or quarrel with him, he should say, "I am fasting")).

The Prophet (sal-Allaahu `alayhe wa sallam) also said (on the authority of Allaah):

((All the deeds of the son of Aadam are for for himself; a good deed is eqaul to ten times it's equivalent except fasting, for certainly it is for Me, and I will give the reward for it. He left his desires, his food, his drink for My sake. There are two pleasures for the fasting person, one at the time of breaking his fast, and the other at the time when he will meet his Lord. The unpleasant smell coming from the mouth of a fasting person is more pleasant to Allaah than the smell of musk)).

The Prophet (sal-Allaahu `alayhe wa sallam) used to announce the good news of the arrival of the month of Ramadhaan to his companions, and would say to them:

((The month of Ramadhaan has come to you. It is the month of blessings. During this month, Allaah sends down mercy, ones mistakes are forgiven, supplications are answered and Allaah praises you in the presence of His angels, so show Allaah your virtues. For certainly the unfortunate individual is he who is prohibited from the mercy of Allaah)).

The Prophet (sal-Allaahu `alayhe wa sallam) said:

(One who does not abandon evil talk and actions, then Allaah is not in need of him abandoning his food and drink (i.e. his fasting)).

(Ref : Fatwa-online)

"Have a blessed month of Ramadhan"