What is the ruling on fasting outside of Ramadan?

Fasting outside of Ramadan (definition) is either obligatory, such as a votive fast, based on the Prophet's (peace and blessings be upon him) saying: "Whoever vows to obey Allah, let him obey Him"; or it is recommended, such as fasting on Mondays and Thursdays, three days of every month, six days of Shawwal, the Day of Ashura, and the Day of Arafah for non-pilgrims; or it is disliked, such as fasting on Friday alone according to the majority of scholars, and on Saturday according to the majority unless it coincides with a customary fast; or it is forbidden, such as fasting on the two Eids and a woman observing a voluntary fast without her present husband's permission.