Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates from the Noble Prophet (peace and blessings be upon him) that he (peace be upon him) said: "A woman should not fast even a single day, apart from the fasts of Ramadan, without her husband's permission while her husband is present at home." Imam Abu Bakr (may Allah have mercy on him) says that the statement of the Noble Prophet (peace be upon him), "apart from the month of Ramadan," is of the same type about which we say that when a ruling is based on a reason, and the reason is present and established, then the knowledge and obligation are established. Therefore, when the Noble Prophet (peace be upon him) declared it permissible for a woman to observe the fasts of Ramadan without her husband's permission, because the fasts of Ramadan are obligatory upon her, then every obligatory fast is permissible for her to observe without her husband's permission. I have written a separate book on this issue, in which I have explained those commands and prohibitions that are based on a reason.