THE OBLIGATION OF FASTING
Allah says in the Quran:
"O uou who have faith! Fasting is prescribed for you as it was prescribed for those before you - so that hopefully you will have taqwa." - Al Baqarah(2):183
Meaning that hopefuly you can safeguard yourselves from the Fire through Fasting; fasting is a means to the forgiveness of sins, and sins lead one to the fire.
The two sahihs record the hadith in which the prophet (pbuh) said:
"Islam is built upon five: that you worship Allah and reject the worship of anything else, to establish the prayer, the giving of Zakat, performing pilgrimage to the house and Fasting the month of Ramadan." [This is the wording of Muslim, Bukhari has the first sentence as 'that you testify none has the right to be worshipped save Allah'].
THE VIRTUES OF FASTING
Fasting carries with it a number of benefits, amongst which are: the elevation to ones rank, the expiation of sins, the breaking of ones desire and lusts, the increase of charity, the multiplication of actions of obedience to Allah, giving thanks to the one who knows the hidden matters, and preventing oneself from even contemplating the commiting of sin.
THE ELEVATION OF RANK
With regards to the elevation of rank, the Messenger of Allah (pbuh) said:
"When Ramadan comes, the gates of Paardise are opened, the gates of Hellfire are locked and devils are chained." [Bukhari]
He (pbuh) also said, relating from his lord Mighty and Magnificient,
"All of the actions of the son of Adam are for him except the fast for that is for me and I will reward it. Fasting is protecting sheild, so when it is the day when one of you are fasting, let him not behave or speak indecently; if someone tries to abuse him or fight him, let him say, 'I am fasting'. By the one in whose hand is the soul of Muhammad, the smell emanating from the mouth of the one fasting is better with Allah then the smell of musk. The one fasting has tewo time of joy, when he breaks his fast he is happy and when he meets his lord he will rejoice at his fasting." [Bukhari and Muslim]
The prophet (pbuh) also said:
"Every action that the son of Adam does, [its reward] will be multiplied, a good deed will be increased tenfold. Allah Mighty and Magnificient says, 'except for the fast, for that is for Me and I will reward it for he left his desires and food for My sake'" [Muslim]
The prophet (pbuh) also said:
"In paradise there is a gate which is called ar-Rayyan through which the people who fasted will enter on the day of Judgement, and no one else shall enter along-side them. It will be asked, 'where are those who fasted?' and they will walk through it, and upon the entry of the last of them, it will be locked, and no one else will walk through it." [Bukhari and Muslim]
With regards the 'opening of the gates of paradise', this is a phrase that points to the increase of actions of obedience that in turn lead to the opening of the gates of Paradise. 'Locking the gates of Fire' is a phrase that points to the decrease, and lack of therewith, of sins which in turn leads to the locking of the gates of the Fire. 'The chaining of the devils' is a phrase that points to the termination of their whisperings, and temptations, to those who are fasting because they give up hope of receiving a favorable response.
His saying, "All of the actions of the son of Adam are for him except the fast for that is for me, and I will reward it," fasting has been specifically adjoined to him in the order of Honour it because the hidden nature of fasting prevents ostentation entering it, and moreover, hunger and thirst are not used as means to draew closer to any king of this world nor any idol.