* Narrated Ibn 'Abbas:It is interesting that Muhammad fasted because he saw Jews fasted and someone explained it to him. He didn't know about it before this incident, and there is no indication that Allah had sanctioned it.
When the Prophet came to Medina, he found (the Jews) fasting on the day of 'Ashura' (i.e. 10th of Muharram). They used to say: "This is a great day on which Allah saved Moses and drowned the folk of Pharaoh. Moses observed the fast on this day, as a sign of gratitude to Allah." The Prophet said, "I am closer to Moses than they." So, he observed the fast (on that day) and ordered the Muslims to fast on it. (Sahih Bukhari 4.609, and Sahih Muslim)
* ``[Jesus said:] When you fast, do not look somber as the hypocrites do, for they disfigure their faces to show men they are fasting... But when you fast, put oil on your head and wash your face, so that it will not be obvious to men that you are fasting, but only to your Father, who is unseen; and your Father, who sees what is done in secret, will reward your.'' (Matthew 6:16,18)
Ramadan begins on sighting of new moon in the west by 2 reliable Muslims, or by any large group of people, or if the previous month has completed 30 days. Fasting begins at dawn when white thread can be distinguished from black.
Every Muslim of sound mind and physically able must fast, except the aged, the very sick, nursing and expectant mothers, and those making long trips. Women must not fast during menstruation.
The niat (intention) must be said before dawn of the first day, like: "I intend to keep the fast of Ramadan". If the fast is broken, niat must be repeated.
During fasting from dawn to sunset, not allowed to eat, drink, smoke, or sex. Not to swallow own saliva or vomit, if possible. Encouraged eat a little meat before dawn, bathe more often, avoid useless and evil talk, do pious deeds, have devotions in mosque, memorized Qur'an, obey parents, be kind to wives, avoid quarrelling.
If fast is accidentally broken, can be made up, else need to give 60 destitude persons a measure of grain, or free a slave, or fast two consecutive months.
Fasting is recognized as physically demanding but spiritually rewarding.