Sleeping today is not prohibited for him. Rather, it causes sleeping to be prohibited for him tomorrow, because when one is not careful, it is only with regard to a condition. In the former case, sleeping on the second day merely fulfills the condition on which the prohibition was based, causing it to take effect retroactively. Therefore, there is concern that he will not be careful and retroactively cause a violation. However, one is careful with regard to a prohibition. In the latter case, sleeping on the second day is directly prohibited. Therefore, there is no concern that he will violate the prohibition.

The Gemara raises a difficulty with regard to the opinion of Rav Yehuda: We learned in the mishna that one who says: Sleeping is konam for me, or: Walking is konam for me, or: Speaking is konam for me, may not violate his vow. What are the circumstances? If we say that the wording of the vow is precisely as the mishna teaches, is the vow: Sleeping is konam for me, a valid vow? But didn’t we learn in a baraita: There is stringency with regard to oaths vis-à-vis vows, in that oaths apply to something that has actual substance and to something that does not have actual substance, which is not the case with regard to vows. And sleep is something that does not have actual substance, so how can a vow apply to sleep? Rather, the mishna must be referring to a case where he said: Sleeping is konam for my eyes.

The Gemara questions this interpretation: And if he did not give a measurement to the prohibition created by the vow, but rather prohibited himself from sleeping for an unlimited period of time, do we let him be until he inevitably transgresses the prohibition: He shall not profane, by falling asleep? But didn’t Rabbi Yoḥanan say that if one says: I hereby take an oath that I will not sleep for three days, the court flogs him for taking an oath in vain, and he may sleep immediately, as he is incapable of fulfilling his oath? Here too, if the prohibition has no time frame, the vow should not take effect.

Rather, the mishna must be referring to a case where one said: Sleeping is konam to my eyes tomorrow if I sleep today. The mishna rules that he may not sleep today, lest he transgress the prohibition of: He shall not profane, by sleeping tomorrow. However, didn’t you say that with regard to this vow it is agreed that he may sleep today, as one is careful with regard to any direct prohibition and will not violate the vow tomorrow? If so, why is it prohibited for him to sleep today?

Rather, it is obvious that the mishna is referring to a case where one said: Sleeping is konam to my eyes today if I sleep tomorrow. The Gemara asks: And if he does not sleep today, when he sleeps tomorrow, what transgression of: He shall not profane his word, is there? Rather, is it not with regard to a case where he slept on the first day, and therefore the mishna warns him not to sleep on the second day lest he transgress the prohibition retroactively? Apparently, there is a situation in which he sleeps on the first day. And this is a refutation of the opinion of Rav Yehuda that he may not sleep today lest he sleep tomorrow as well, thereby violating the prohibition.

The Gemara answers: When the mishna teaches that he may not sleep tomorrow, it does not mean that today he may sleep ab initio. Rather, it means that if he did sleep today he must be careful not to sleep tomorrow.

Ravina said a different answer: Actually, the mishna may be interpreted as it teaches, i.e., sleeping is konam for me. The vow does not take effect, as sleep does not have actual substance. And if so, what is the reason the mishna states that if he sleeps he is in violation of the prohibition: He shall not profane? He transgresses the prohibition by rabbinic law. Although the vow does not take effect by Torah law, the Sages prohibited him from breaking his word.

The Gemara asks: But is there a prohibition of: He shall not profane, by rabbinic law? The Gemara answers: Yes, and it is taught in a baraita: With regard to matters that are permitted, but others are accustomed to observe a prohibition with regard to them, you may not permit these matters before those people, as it is stated: “He shall not profane his word” (Numbers 30:3). If they contravene their custom they are in violation of the prohibition: He shall not profane his word, by rabbinic law, as that is similar to violating a vow.

The Gemara attempts again to raise a difficulty with regard to Rav Yehuda’s opinion. We learned in a mishna (57a) that if a man said to his wife: Deriving benefit from me until Passover is konam for you if you go to your father’s house until the following festival of Sukkot, then, if she went to her father’s house before Passover, she is prohibited from deriving benefit from him until Passover, as she violated the condition, thereby enabling the vow to take effect.

The Gemara infers: Only if she went before Passover is it prohibited for her to derive benefit from him. However, if she did not go, she is not prohibited from deriving benefit from him. Apparently, even though she can transgress the condition retroactively until Sukkot by going to her father’s house, there is no concern that she will do so. This is difficult according to Rav Yehuda, who prohibits transgression of a conditional vow that may take effect retroactively.

Rabbi Abba said that the baraita can be interpreted as follows: If she went before Passover, she is prohibited from deriving benefit from him, and if she does so she is flogged. If she did not go before Passover, it is merely prohibited for her to derive benefit from him, lest she violate the condition and cause the vow to take effect retroactively. However, she is not liable to be flogged for it, as the vow has not yet taken effect.

The Gemara counters: Say the latter clause of that mishna, which states that if she goes to her father’s house after Passover she is in violation of: He shall not profane his word. And if the mishna is referring to a case where she did not derive benefit from him before Passover, is there a transgression of: He shall not profane? Clearly the vow was not violated. Rather, it is obvious that she derived benefit from him before Passover, and therefore if she goes to her father’s house between Passover and Sukkot she violates the vow retroactively. Apparently, she may derive benefit from him, even though she can subsequently violate the vow by transgressing the condition.