It was only by coincidence, but here he intended it through the vow, so his vow is not binding, and it falls under his (peace be upon him) saying: "There is no vow in disobedience" (11). It is also deduced that he is not obligated to do anything, based on the vow of disobedience mentioned earlier. If a woman vows to fast on the day of her menstruation or postpartum bleeding, she must offer expiation [and nothing else] (12). I do not know of any disagreement among our companions regarding this.

1860 - Issue: He said: (And if his arrival coincides with one of the days of Tashriq, he shall fast it, according to one of the two narrations from Abu Abd Allah, may Allah have mercy on him. The other narration is that he does not fast it, and he shall fast a day in its place, and he shall offer the expiation of an oath.)

There is a difference of opinion narrated from Ahmad, may Allah have mercy on him, regarding fasting the days of Tashriq for an obligatory fast, and we have mentioned that in [the book of] Fasting (1). If we say: He fasts them for the obligatory fast, then he fasts them here, and it suffices him. And if we say: He does not fast them, then his ruling is the ruling of one whose arrival coincides with the day of Eid, which has already passed.

Section: And if he says: "I have vowed to Allah to fast the day [in perpetuity] that such-and-such person arrives," or he says: "I have vowed to Allah to fast every Thursday in perpetuity," then that becomes obligatory upon him for the future. As for the day on which he arrives, the explanation of its ruling has already passed, and that day does not enter into his vow if it falls within the month of Ramadan; because it is inconceivable that Ramadan could be separate from the inclusion of that day, and he cannot fast it for anything other than Ramadan; because that would not be accepted. It follows from the opinion of al-Khiraqi that it does enter into his vow, and his fasting suffices him for both Ramadan and his vow. And if it coincides with a day of Eid, or a day of the days of Tashriq, or a day of menstruation, there is [in it] (2) the disagreement that has already passed. And if he is obligated to fast two months for the expiation of Dhihar (injurious assimilation) or the like, he shall fast them for the expiation, not for the vow; because whenever he intends the vow at the beginning of them, the succession (tatabu') is broken, so he is unable to perform the expiation. Then, he makes up his vow and offers expiation; because he abandoned the fasting of the vow while it was possible to perform it for an excuse. This differs from the days that fall within Ramadan, for they do not enter into his vow due to the impossibility of separating them from it, whereas here, the days can be separated from the inclusion of the expiation.