As for the fourth pillar, the Prophet said: “and to fast the month of Ramadan.”
Ramadan is the month that comes between Shaʿban and Shawwal. It was given this name, according to one view, because when the Arabs first named the months it happened to coincide with the peak of scorching heat (ramdāʾ), so it was called Ramadan. Another view is that it was so named because it extinguishes the burning heat of sins, for sins are themselves fiery.
The Messenger of Allah ﷺ stated: “Whoever fasts Ramadan out of faith and in hope of reward will have his past sins forgiven.”
What matters here is that this month is well-known to Muslims; Allah—glorified and exalted—is He—mentions it explicitly in His Book: “The month of Ramadan in which the Qur’an was revealed” (al-Baqarah 2:185). No other month is named in the Qur’an besides this one.
Fasting Ramadan is a pillar of Islam, and Islam is not complete without it. Nevertheless, it is obligatory only upon those who meet the following six conditions:
- Being Muslim;
- Having reached puberty;
- Possessing sound intellect;
- Being able to fast;
- Being resident (not traveling);
- Being free of any legal impediment.
If a person is a child, fasting is not required of him. If he is insane, it is not required. If he is an unbeliever, it is not required. If he is unable to fast, this inability falls into two categories:
a) If the inability is expected to disappear—such as a temporary illness—he breaks his fast and later makes up the same number of days he missed.