Allaah says in the Qur'aan what may be interpreted as, "O' you who believe, fasting is prescribed for you as it was prescribed for those before you so that you may achieve Taqwaa. Fasting the month of Ramadan is one of the main pillars of Islam. It is obligatory upon every sane, healthy Muslim whose reached puberty and is not traveling during the time of fasting. As for women, they must not fast if they are menstruating or having post-childbirth bleeding.
* Intentional Eating or Drinking
If someone eats or drinks due to forgetfulness, a mistake, or coercion, then his fast is still valid and should continue to fast. If you choose to eat or drink, for any reason, then your fast will become invalid.
* Intentional Vomiting If one is overcome by the urge to vomit, and vomits unintentionally, then he should continue to fast. If someone chooses to vomit, for any reason, then his fast will become invalid.
* Intentional Sexual Intercourse If one has sexual intercourse while fasting, then he must perform kaffaarah, expiation of the sin. (Fasting continuously for sixty days or if unable then one should feed sixty poor people).
* Menstrual or Childbirth Bleeding The fast becomes invalid during menstrual or post-childbirth bleeding. Even if such bleeding begins just before sunset, the fast of that day is invalid and the day must be made up at a later time.