As-Sawm (Fasting in Month of Ramadan) Almighty says:
O you who believe! Observing As-Sawm (the fasting) is prescribed for you as it was prescribed for those before you, that you may attain piety. (Surah Al-Baqarah 2: 183)
For certain periods at a time, the Muslim trains himself to curb his desires, desires that are even lawful. By fasting one not only benefits spiritually, but physically as well. One of the spiritual benefits of fasting is that one feels for those from among his Muslim brothers who are poor, and who spend long periods of time without food or drink, such as is happening to many of our brothers around the globe.
Ramadhan is the best month of the year, the month in which Allah revealed the Qur'an:
The month of Ramadhan in which was revealed the Qur'an, a guidance for mankind and clear proofs for the guidance and the Criterion (between right and wrong) (Surah Al-Baqarah 2: 185)
In it is a night that is better than one thousand months. Allah Almighty says:
Verily! We have sent it (this Qur'an) down in the night of AI¬-Qadr (Decree). And what will make you know what the night of AI-Qadr (Decree) is? The night of AI-Qadr (Decree) is better than a thousand months. (Suran Al-Qadr 97:1-3)
If one fasts Ramadhan with faith, seeking his reward from Allah, then his previous sins are forgiven.
In an authentic Hadith related by Abu Hurairah (Radhi Allahu Anhu), the Prophet (Sallallahu Alayhi wa Sallam) said:
Whosoever fasts the month of Ramadhan, having faith and seeking his reward from Allah, then he will be forgiven for his previous sins. Whosoever stands (to perform the voluntary night prayer) in Ramadhan, having faith and seeking his reward from Allah, he will be forgiven his previous sins. And whosoever stands (to pray at night) on the night of Qadr, having faith and seeking his reward from Allah, he will be forgiven his previous sins. (Agreed upon)
When one is fasting, one must also especially avoid backbiting, spreading false tales, lying, or listening to music or false speech; moreover, one should especially stay away from all forbidden deeds. The one who is fasting should, based on the Sunnah, recite the Qur'an more often, remember Allah, give charity, and strive more to worship Allah, especially during the last ten days of the month.
Shaikh Muhammad bin Salih Al-'Uthaimin (Rahimallullah) said:
Indeed fasting is one of the pillars of Islam and one of its great foundations. Allah Almighty says:
O you who believe! Observing As-Sawm (the fasting) is prescribed for you as it was prescribed for those before you, that you may attain piety. [Fasting] for a fixed number of days, but if any of you is ill or on a journey, the same number (should be made up for) from other days. And as for those who can fast with difficulty, (the elderly, etc.), they have (a choice either to fast or) to feed a Miskin (poor person) (for every day). But whoever does good of his own accord; it is better for him. And that you fast, is better for you if only you know. The month of Ramadhan in which was revealed the Qur'an, a guidance for mankind and clear proofs for the guidance and the Criterion (between right and wrong). So whoever of you sights (the crescent on the first night of) the month (of Ramadhan, i.e., is present at his home), he must observe Sawm (fasts) that month, and whoever is ill or on a journey, the same number [of days which one did not observe Sawm (fasts) must be made up for] from other days. Allah intends for you ease, and He does not want to make things difficult for you. (He wants that you) must complete the same number (of days), and that you must exalt Allah [to say ''Allahu Akbar" (Allah is the Most Great) on seeing the crescent of the months of Ramadhan and Shawwal] for having guided you so that you may be grateful to Him. (Surah Al-Baqarah 2: 183-185) The Prophet (Sallallahu Alayhi wa Sallam) said:
Islam is built on five: to bear witness that none has the right to be worshipped but Allah and that Muhammad is the Messenger of Allah, to establish the prayer, to give Zakat, Al-Hajj to the House (the Ka'bah), and to fast the month of Ramadhan. (Agreed upon)
And in the narration of Muslim, the order is different:
To fast the month of Ramadhan, Ai-Hajj to the House (the Ka'bah).
There is a consensus among the Muslims that it is obligatory to fast the month of Ramadhan; the knowledge thereof is one of those matters that are necessary to know as a Muslim. Whoever denies its being compulsory has disbelieved and must be asked to repent. If he repents and admits that it is compulsory, then all is well; otherwise, "he is killed as a disbelieving apostate: he is neither washed, nor , enshrouded; he is not prayed for, nor do others supplicate to Allah for having mercy on him. He is to be buried quickly so that people are not harmed by his awful smell and so that his family is not harmed by having to look at him.
Fasting was prescribed two years after the Hijrah (migration to Al¬Madinah), and so the Prophet (Sallallahu Alayhi wa Sallam) fasted Ramadhan for nine years.
Fasting was prescribed in two stages: 1) Muslims were given a choice between fasting and feeding a poor person, yet fasting was made preferable.
2) Without being given a choice, Muslims were ordered to fast.
Salamah bin Akwa' (Radhi Allahu Anhu), said, 'When this verse was revealed:
And as for those who can fast with difficulty (the elderly, etc.), they have (a choice either to fast or) to feed a Miskin (poor person) (for every day) (Surah Al-Baqarah 2: 184)
Whoever wished to break their fast did so (by feeding a poor person) until the following verse was revealed, abrogating the previous one."
By the following verse, he meant:
So, whoever of you sights (the crescent on the first night of) the month (of Ramadhan, i.e., is present at his home), he must observe Sawm (fasts) that month, and whoever is ill or on a journey, the same number [of days which one did not observe Sawm (fasts) must be made up for] from other days. (Surah Al-Baqarah 2: 185) [/center]
So, Allah made fasting obligatory on each individual, without a choice. The fast is not compulsory until the month of Ramadhan begins, which also means that one should not fast the days before Ramadhan begins, for the Prophet (Sallallahu Alayhi wa Sallam) said:
Let not one of you precede by fasting one or two days (before Ramadhan begins) except for a man who habitually fasts that day, then let him fast on that day. (Recorded by Al-Bukhari)