Sawm, or fasting, means abstaining from food, drink and sexual relations from dawn until sunset, with the intention of worshipping Allah. The obligatory fast is the fast of the month of Ramadan, and it is one of the five pillars of Islam.

The Qur'an explains its purpose. In Surah Al-Baqarah, chapter two, verse one hundred and eighty-three, an English translation of the meaning reads: “O you who have believed, decreed upon you is fasting as it was decreed upon those before you that you may become righteous”. Two verses later, it says: “The month of Ramadhan is that in which was revealed the Qur'an, a guidance for the people and clear proofs of guidance and criterion.” And the same verse reminds us: “Allah intends for you ease and does not intend for you hardship”.

The hadith add to this. Ibn Umar reported that the Prophet, peace be upon him, said Islam is based on five principles, the last of which is to observe the fast of Ramadan, in Sahih al-Bukhari, number eight. In a report where the Prophet speaks of what Allah has said, fasting is singled out: all the deeds of the children of Adam are for them, except fasting, which is for Allah, and He will give its reward. The Prophet also said that fasting is a shield, and that a fasting person should avoid foolish talk and quarrelling, and, if someone abuses or fights him, should simply say, “I am fasting.” That is in Sahih al-Bukhari, number nineteen hundred and four. So fasting includes guarding the tongue and behaviour, not only staying away from food and drink.

Now the basics. The fast runs from the true dawn, the start of Fajr, until sunset. The Qur'an describes eating and drinking until the white thread of dawn becomes distinct, and then completing the fast until night. The intention is made in the heart, and does not need to be spoken. Deciding that you will fast tomorrow, or getting up for the pre-dawn meal, shows it. And the fast is required of a Muslim who is adult, of sound mind and able, and who is not travelling or ill. Children are often introduced to it gradually, so they learn it with ease.

Scholars differ on two points. First, how the start of Ramadan is determined: by local moon sighting, sighting anywhere in the world, or astronomical calculation. Follow the announcement of your local mosque or community. Second, the timing of the intention. The Shafi'i and Hanbali schools require it before dawn each night for an obligatory fast, the Maliki school accepts a single intention at the start of the month, and the Hanafi school allows it up to before midday if nothing has been eaten. Follow your school or local teacher.