Hi, does a kabalh in a dream have any halachic significance ?
And if yes, is the mesiros mo’dah made on erev rosh hashana m’vatel the kabalh/neder?
Thank you for your question.
A neder or shvuah that a person made while dreaming is controversial is it is binding or not. Essentially, we hold like the Rosh (Teshuvas Harosh 8-11) that it is not binding, (see Levush Y:D 210-4, Maharal, Shulchan Aruch Y:D 210-2) however since there are Rishonim (Rashba 1- 331) who hold that it is, the person should be careful about it and make hataras nedarim for that neder. In fact, it is preferable to do the hatara in front of 10 people, however if that is difficult, it can be done in front of three.
If the neder was to do a mitzva, such as to pay back a creditor, which is a mitzva then the person has to keep to his neder according to all opinions. The reason for this is not because of a neder rather because it is a sign from heaven that he should do what he has to do. (see Pischei Teshuva Y:D 210-2 in the name Radvaz). However, if it was a neder to keep something that isn’t a clear mitzva rather a midas chasidus, and not an obligation, (not eating gebotz on Pesach, or not to talk while wearing his teffilin) then you can be matir this neder (see Pichei Teshuva ibid 3, Kol Nidrei 56-8 and ftnt 19).
However if a neder b’chalom was specifically included in your mesiras moda’ah then it is included and you don’t have to be concerned about it. (Shut Shemesh Tzedakah Y:D 5, Kol Nidrei 56-17 ftnt. 36, this is even though it was kabala l’dvar mitzva.)