Firstly: Fasting the Days of Eid
It is haram to fast on the two days of Eid: al-Fitr and al-Adha. Consensus has been quoted over this by: Abu Ja`far al-Tabari, Ibn al-Mundhir, al-Tahawi, Ibn Hazm, Ibn `Abd al-Barr, Ibn Rushd, Ibn Qudamah, and al-Nawawi.
Secondly: The Days of Celebration
1. The dates of the days of celebration
The days of celebration are the eleventh, twelfth, and thirteenth of the month of Dhu al-Hijjah.
2. The ruling of fasting the days of celebration
It is haram to fast the days of celebration.  Malikis, Hanbalis, and al-Shafi`i in his old position, all excepted the pilgrim who was not able to sacrifice, then he may fast them, and this is the position of some of the Salaf. This is by agreement of the four schools of jurisprudence, the position of the Zahiris, and the majority of scholars.
Thirdly: Fasting the Day of Doubt
1. Defining the day of doubt
The day of doubt is the thirtieth of Sha`ban if the moon was not legally sighted the night before.
2. The ruling of fasting the day of doubt
It is haram to fast the day of doubt with the intention that it is in case it's the first of Ramadan or to error on the side of caution. This is the position of the Malikis, Shafi`is,  Except that the day of doubt has a meaning for them, where al-Nawawi said: “Our companions said: ‘the Day of Doubt is the thirtieth day of Sha`ban, and it is so if the people started to have mention among them that it has been sighted yet no just witness said so, or he did state it but his sole witness account was rejected, or a number of young boys and women said it, or some number of transgressors and slaves, and this is what makes it a day of doubt for our companions, without difference among them. As for if none of this took place, then it is not a day of doubt, regardless whether the sky is clear or cloudy. This is the school’s position.” Al-Majmu` (401/6) a narration from Ahmad, and a group of the Salaf. It is also the choice of al-Jassas, Ibn Hazm, Ibn `Abd al-Barr, and Ibn `Uthaymin.
Fourthly: The Woman Fasting Voluntarily Without her Husband's Permission
1. The ruling of a woman fasting voluntarily without her husband's permission
It is haram for the woman to fast voluntarily without her husband's permission, and this is by agreement of the four schools of jurisprudence.  Malikis have made it haram only if the husband has a need for his wife. For the Shafi`is, if the woman fasts without her husband’s permission, then it is valid but she is sinful. Sinfulness for them is for any day that may be repeated, but for days that may not, like `Arafah, then she may fast without his permission, except if he prohibits her.
2. The ruling of a man breaking his wife's voluntary fast without her permission
If a woman fasts voluntarily without her husband's permission then he may break her fast if he has need of her. This is by agreement of the four schools of jurisprudence.  Malikis have explicitly mentioned that he may break her fast through intercourse only, as for food or drink, then this is not for him to do.