Nedarim 12 - 18
Days of Sleeplessness
How long can a human survive without any sleep? The answer supplied by Rabbi Yochanan in our gemara has a number of applications throughout the Talmud.
If a person takes an oath that he will not sleep for three days, we relate to his oath differently than if he took an oath to abstain from sleep for one or two days, or to abstain from food for even three days. In the former case his oath is considered invalid because he has committed himself to something which is impossible for him to fulfill. Therefore, he immediately receives lashes for taking a vain oath. He may sleep at once, as he is not bound by this oath.
This biological limitation on sleeplessness is cited elsewhere (Mesechta Yevamot 121b) in regard to an incident related by Rabbi Meir about a man who fell into a deep pool and surfaced alive after three days underwater. This sage proposed this as support for his opinion that even if a man falls into a body of water, all of whose shores are visible to us, we cannot testify that he is dead and that his wife may remarry. The majority of the sages, however, rule that such a body of water is not like an ocean or large lake where it may be suspected that the missing person came ashore far away from our range of vision. Since we would have seen him had he come ashore, we can assume that he drowned, and the incident cited by Rabbi Meir must be dismissed as a miracle rather than proof that one can survive for so long under water.
Why, asks the gemara, is it unnatural to survive for three days in the water? It cannot be because of not eating for so long a period, because we find that the Jews in Shushan fasted for three days and nights (Megillat Asther 4:16) to deserve the Purim miracle. The unnaturalness of the survival, concludes the gemara, was in the fact that he did not sleep for three days.
Another reference to sleeplessness for three days is found in the account of the seven-day Simchat Beit Hashoeva celebrations which took place in the Beit Hamikdash on the Festival of Succot. Rabbi Yehoshua ben Chanina describes the busy schedule that he and his fellow Levites had in those days. After a day filled with sacrificial service, prayers and a holiday meal, they spent the night in the festivities surrounding the drawing of the water for the special Succot libations on the altar. His statement that "when celebrating Simchat Beit Hashoeva we did not sleep" is challenged by the gemara on the basis of Rabbi Yochanan's definitive ruling that one cannot survive without sleep for even three days, let alone seven. The answer given is that Rabbi Yehoshua and his colleagues did not enjoy a real sleep during those festive days, but they certainly dozed off in snatches upon each other's shoulders.
When a Benefit is Not a Benefit
How do we view the benefit which a Jew derives from the fulfillment of a mitzvah? Although the reward for such fulfillment is immeasurable, it is not considered a benefit when relating to matters in which deriving benefit is forbidden. This is clearly expounded by the Sage Rava (Mesechta Rosh Hashana 28a) in regard to one who takes the horn of a sacrificial animal and blows into it to fulfill the mitzvah of shofar on Rosh Hashana. Even though it is forbidden to derive any benefit from any part of an animal consecrated as a sacrifice, the benefit which one derives from fulfilling a mitzvah is not considered a benefit, and his fulfillment of the mitzvah is therefore in order. Similarly, if one has taken a vow not to derive any benefit from an ordinary shofar, he may still use it for the mitzvah.
There is one problem, however, in regard to applying Rava's rule to sitting in a Succah. Only a daf earlier (15b) the Ran cites a gemara (Rosh Hashana ibid.) which states that if one has taken a vow not to benefit from a certain spring, he may immerse himself in it for a tevila (immersion) of mitzvah in the winter but not in the summer. The reason is that in the winter, his only benefit is the spiritual one of mitzvah fulfillment, whereas in the summer he has the added physical benefit of cooling off. Should this not also disqualify sitting in a Succah from which he is prohibited to benefit because of his vow, since he also enjoys the physical benefit of shade from the sun? The answer is that since he has a home in which he could enjoy the same protection from the sun, his sitting in a Succah is not considered a physical benefit to him.