Does an oath (shevua) to fast on Rosh Chodesh take binding effect?
Synopsis
Whether a shevua to fast on Rosh Chodesh takes effect depends on whether the prohibition of fasting on Rosh Chodesh is biblical or rabbinic — with major authorities in dispute. A shevua that includes Rosh Chodesh within a broader series takes effect via the principle of issur kolel.
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Is fasting on Rosh Chodesh forbidden, and what is the source of the prohibition — biblical or rabbinic?
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