Siman 569

An individual who vowed to fast over some distress and began to fast, and the distress passed in the middle of the day – nevertheless, he is obligated to complete the fast. And not only that, but even if he fasted for a sick person that they should recover, and the sick person died – nevertheless, he is obligated to complete the fast. And not only that, but even if he accepted upon himself many fasts – he is obligated to fast all of them. And we do not say: behold, we are witnesses that he only accepted them with the intent that the sick person should recover, for ultimately these are matters of the heart and they are not matters, since he accepted the fasts without specification. And certainly if he said "Behold, I accept the fasts on the condition that the sick person recovers" and they died – he is exempt from fasting. But if he accepted the fasts upon himself without specification – he is obligated.

And so too one who vows to tzedakah on behalf of a sick person: if he said, "I hereby vow to tzedakah on behalf of this sick person on the condition that he recovers," and he died—he is exempt, and only what he gave, he has given. But if he said, "I hereby vow such and such to tzedakah on behalf of this sick person," and he died—he is obligated to pay everything that he vowed; even though we are witnesses that he only vowed on the condition that he recovers, nevertheless, they are matters of the heart, and they are not matters.

But regarding a community, it is not so. For if the community fasted over a matter and were answered before midday—they do not complete it. As we learned in a Mishnah regarding fasts for rain at the beginning of the third chapter of Taanit (19a): because we do not burden the community excessively. And also, regarding a community, the heart of the beit din stipulates for them that if the distress passes before midday—they do not complete it. And all the more so a community that fasted for a sick person and he died, that they do not need to complete it. Nevertheless, if the talmidei chachamim and the majority of the community wish to complete it—an individual is not permitted to separate himself from them. (See Magen Avraham, subsection 1, who wrote that according to the opinion of the Rosh, when he dies they must complete it. And in my humble opinion it is not so. And it is an a fortiori argument. And that which he wrote "and were answered," is because he is dealing with such a case similar to rain. Furthermore: that it is not his desire to mention a bad thing. But he does not disagree with the Ran. And so it is in the wording of the Tur and the Shulchan Aruch. And examine carefully and you will find it simple.)

However, when an error is discovered in the very acceptance of the fast—even for an individual, he is exempt from completing it. For example, an individual who fasts over a distress, and it became known that before the acceptance of the fast the distress had already passed, or the sick person died—behold, he does not need to complete the fast, and likewise the tzedakah that he vowed on behalf of the sick person, because the acceptance or the vow was in error. And all the more so a community that heard, even after midday, that the distress had already passed, that they do not need to complete it, for an acceptance in error is nothing.