Some of the Ahkaam (Rulings) on fasting

6) there is the kind of fasting that must be done on consecutive days, like fasting in ramadaan, or fasting to expiate for killing someone by mistake, divorcing one’s wife by zihaar [a jaahili form of divorce in which a man says to his wife, “you are to me as the back of my mother” – translator], or having intercourse during the day in ramadaan. also, one who makes a vow to fast consecutive days must fulfil it.

there is also the other kind of fasting which does not have to be done on consecutive days, such as making up days missed in ramadaan, fasting ten days if one does not have a sacrifice, fasting for kafaarat yameen (according to the majority), fasting to compensate for violating the conditions of ihraam (according to the most correct opinion), and fasting in fulfilment of a vow in cases where one did not have the intention of fasting consecutive days.

(7) voluntary fasts make up for any shortfall in obligatory fasts. examples of voluntary fasts include ‘aashooraa, ‘arafaah, ayyaam al-beed [the 13th, 14th and 15th of the hijri months – translator], mondays and thursdays, six days of shawwaal, and fasting more during muharram and sha’baan.

(8) it is not permitted to single out a friday for fasting (al-bukhaari, fath al-baari, no. 1985), or to fast on a saturday, unless it is an obligatory fast (reported and classed as hasan by al-tirmidhi, 3/111) – what is meant is singling it out without a reason. it is not permitted to fast for an entire lifetime, or to fast for two days or more without a break, i.e., to fast two or three days without a break in between.

it is haraam to fast on the two eid days, or on the ayyaam al-tashreeq, which are the 11th, 12th and 13th of dhoo’l-hijjah, because these are the days of eating and drinking and remembering allaah, but it is permissible for the one who does not have a sacrifice to fast them (ayyaam al-tashreeq) in mina.