Categories of rulings onfasting

What are the categories of rulings on fasting?.
Praise be to Allaah.
The categories of rulings are five: obligatory (waajib), forbidden
(muharram), encouraged (mustahabb), disliked (makrooh) and permissible
(mubaah). These five rulings have been narrated with regard to
fasting. We cannot list everything that comes under each of these
rulings, but we will mention what we can.
1 – Obligatory fasts
(i) The Ramadaanfast
(ii) Making up missed Ramadaan fasts
(iii) Expiatory fasts (expiation for accidental killing,
expiation for zihaar (a form of jaahili divorce), expiation for having
intercourse during the day in Ramadaan, andexpiation for breaking an
oath)
(iv) Fasting for the pilgrim who does tamattu' in Hajj if
he does not have a sacrificial animal. "and whosoever performs the
'Umrah in the months of Hajj, before(performing) the Hajj, (i.e.
Hajj-at-Tamattu' and Al-Qiraan), he must slaughter a Hady such as he
can afford, but if he cannot afford it, he shouldobserve Sawm (fasts)
three days during the Hajjand seven days after his return (to his
home)" [al-Baqarah 2:196 – interpretation of the meaning].
(v) Fasting in fulfilment of a vow
2 – Mustahabb (encouraged) fasts
(i) Fasting the day of 'Ashoora'
(ii) Fasting the dayof 'Arafah
(iii) Fasting on Mondays and Thursdays each week
(iv) Fasting three days of each month
(v) Fasting six days of Shawwaal
(vi) Fasting most of the month of Sha'baan
(vii) Fasting the month of Muharram
(viii) Fasting alternatedays – which is the best offasting
All of these are proven in hasan and saheeh ahaadeeth, and may be
found on this site.
3 – Makrooh (disliked) fasts
(i) Singling out Friday for fasting – because the
Prophet (peace and blessings of Allaah be upon him) said: "Do not fast
on a Friday unless you fast a day before or a day afterwards." Agreed
upon
(ii) Singling out Saturday for fasting – because the
Messenger (peace and blessings of Allaah be upon him) said: "Do not
fast on Saturdays apart from days when you are obliged to fast, even
if one of you cannot find anything other than grape stalks or the bark
ofa tree (to suck on, to make sure that he is not fasting)." Narrated
by al-Tirmidhi, 744, who classed it as hasan. Also narrated by Abu
Dawood, 2421; Ibn Maajah, 1726; classed as saheeh by al-Albaani in
Irwa' al-Ghaleel, 960.
Al-Tirmidhi said: What is meant by its being makrooh is that a man
should not single out Saturday for fasting because the Jews venerate
Saturday. End quote.
4 – Forbidden fasts
(i) Fasting on Eid al-Fitr, Eid al-Adha and thedays of
Tashreeq, which are the three days after Eid al-Adha.
(ii) Fasting on the "day of doubt" – which is the
thirtieth of Sha'baan, if the sky was cloudy and the new moon could
not be sighted. But if the sky was clear there can be no doubt.
(iii) Fasts observed by women who are menstruating and
bleeding following childbirth.
5 – Permissible fasts – these are fasts that do notcome under any of
the four headings mentioned above.
What is meant by permissible here is that there is no report enjoining
or forbidding fasting on this day in particular, such as Tuesdays and
Wednesdays, even thoughin principle, observing a voluntary fast is an
act of worship that is encouraged.