- Question: [Thursday, 12th Nissan, 5781]
Rabbi, I did not realize that today Thursday is the fast of the firstborn and accidentally ate prior to having heard a Siyum. What am I supposed to do now? Do I still have to fast and/or hear a Siyum? Do I have to make up the fast another day?
You should fast for the rest of the day until you hear a Siyum, and in addition you should redeem the fast with charity.
Explanation: In general, the ruling is that one who accidentally ate on a public fast day is to continue fasting after remembering, and he is not required to make up the fast on another day although should redeem it with charity. Now, the question here is raised regarding a year such as this one in which Pesach falls on Sunday and therefore the fast was pushed up to Thursday, if in such a case he should simply fast on Friday [or hear the Siyum then], or if it retains the same law as above. So, we find a precedent in the Poskim in this matter regarding the only other similar case that this can happen in, which is when Purim falls on Sunday and the fast of Esther was pushed up to Thursday and one accidentally ate on Thursday. In such a case the Poskim rule that he should fast on Friday, which would make it seem that in our case as well he should fast on Friday. However, in truth, the cases of discussion are not similar, as the case that there is discussing one who completely forgot that it is a fast day and only remembered after the day was over on Thursday night, in which case we rule that he could make it up on Friday. However, in this case he remembered during the fast day itself and hence can perhaps still make it up by fasting the rest of the day. Furthermore, some Poskim there rule regarding a Bris that one should never make up the fast on Friday as it has the status of a Taanis Yachid, and if that is the case regarding the fast of Esther than certainly that is the case regarding Taanis Bechoros. Furthermore, some Poskim rule that in a time of need one may redeem the fast of the firstborn with charity, and some even rule that it is even initially permitted to snack on this day. Thus, taking into account all the above, we concluded like the classical ruling that he is to continue to fast and that the fast does not have to be made up despite the above ruling in the Poskim regarding Taanis Esther. Vetzaruch Iyun.
Sources: See regarding fasting the rest of the day and making of the fast on another day: Michaber 568:1; M”A 568:4; Birkeiy Yosef 568; Shaareiy Teshuvah 568:2; P”M 568 A”A 4; M”B 568:2; Kaf Hachaim 549:6-7; 568:7; Piskeiy Teshuvos 568:3; See regarding one who ate on Thursday of the preceded fast of Esther: Shvus Yaakov 3:50, brought in Shaareiy Teshuvah 568:5; M”B 686:3; Kitzur SH”A 141:3; Shevach Hamoadim 136; See regarding leniency’s associated with the fast of the firstborn: Rav Yechiel, brought in Mordechai and M”B 470:2; Peri Hasadeh 4:57; Poskim in Piskeiy Teshuvos 470:11 footnote 52