Besides the Saum of Ramadhan, there are other compulsory Saum as well. These are briefly discussed hereunder.
(1) Saum as Kaffarah for Qasam
When a Qasam (oath) has been violated, one of the options of expiation is to fast three consecutive days. On having fasted three days - one after the other - one is absolved of the sin of having violated the oath.
(2) Saum as Kaffarah for killing
When a person has been accidentally killed, the killer has to fast sixty consecutive days in addition to the Diyat which he has to pay to the heirs of the killed person. (This will, Insha'Allah be explained In Kitabul Jinayat, should Allah Ta'ala grant us the taufeeq to complete this series of books).
(3) Saum of Zihar
When a person utters to his wife. 'You are for me like the back of my mother' or any other similar statement, the wife becomes unlawful to her husband until he has executed the Saum of Zihar which consists of fasting sixty consecutive days. (This subject will, Insha'Allah, be explained In detail when our series reaches Kitabun Nikah).
(4) Saum of Hajj-e-Tamattu
When the Mutamatti is not by the means to sacrifice his/her Dam-e-Tamattu (the animal which a Mutamatti has to compulsorily sacrifice), ten fasts become obligatory in lieu. Three fasts are to be observed in Makkah Muazzamah, the last of the three being on the Day of Arafah, and seven fasts are to be observed after returning home. It is not obligatory to keep these fasts in consecutive order.
(5) There are also some other obligatory fasts which have to be kept as penalties for certain violations of Ihram. These will, Insha'Allah be explained in Kitabul Hajj.