Shabbat 157: Timing of Nullifying a Woman's Vows, Enhancing Mitzvot on Shabbat

Our final Mishna in Massechet Shabbat teaches that a father or husband may nullify his daughter or wife's vows on Shabbat or request that a Sage dissolve vows regarding Shabbat.  We may seal a window on Shabbat to dissolve vows that allow for more joy on Shabbat.  We may measure a rag to figure out whether or not it is large enough to contract ritual impurity and we may measure a ritual bath to determine if it contains enough water for immersion.  

We learn that Rabbi Tzadok's father and Abba Shaul ben Botnit sealed a window using an earthenware vessel and tied and earthenware shard with a long reed-grass with a temporary knot to determine whether or not the roof had an opening the size of a handbreadth.  From their statements and actions we learn that we may seal windows, measure and tie knots on Shabbat.

The Gemarra tells us that Zutei, a student of Rav Pappa, tells us that we may nullify vows on Shabbat for the purpose of bettering Shabbat only.  Rav Ashi looks at the timing of a woman's vow and we are reminded that a father or husband has twenty four hours after learning of this woman's vow to annul it.  The rabbis walk us through examples of the other halachot regarding sealing windows and measuring roofing.  At the end of our daf, we are reminded about measuring only to enhance a mitzvah - Rabba bar Rav Huna was acting "unawares" when he was sitting in a tub without measuring it.  Thus his actions were not prohibited.