the sixth day from their encampment. Rav Aḥa bar Ya’akov said: The sixth day from the start of their journey. They left Refidim and arrived and camped in the desert on the same Sunday. And Rava and Rav Aḥa bar Ya’akov disagree with regard to the mitzva of Shabbat commanded to the Jewish people at Mara, as it is written in the fourth commandment: “Observe the Shabbat day to keep it holy as the Lord your God commanded you” (Deuteronomy 5:11). And Rav Yehuda said that Rav said: As He commanded you in Mara, as it is stated: “There He made for him a statute and an ordinance, and there He proved him” (Exodus 15:25). Their dispute was: One Master held: They were commanded about Shabbat, but they were not commanded about Shabbat boundaries. Therefore, it was permitted to travel from Refidim on Shabbat, because the restriction of Shabbat boundaries was not yet in effect. And one Master held: They were also commanded about the boundaries, and therefore, it was prohibited to leave Refidim on Shabbat.

Come and hear an additional proof with regard to the day of the revelation at Sinai from what was taught in a baraita: In the month of Nisan during which the Jewish people left Egypt, on the fourteenth, they slaughtered their Paschal lambs; on the fifteenth, they left Egypt; and in the evening, the firstborn were stricken. The Gemara asks: Does it enter your mind to say that they were stricken in the evening? Was the Plague of the Firstborn after the Jews left Egypt? Rather, say that the evening before, the firstborn were stricken. And that day was the fifth day of the week. From the fact that the fifteenth of Nisan was a Thursday, the New Moon of Iyyar was Shabbat, as Nisan is typically thirty days long. And the New Moon of Sivan was on the first day of the week, as Iyyar is typically twenty-nine days long. This is difficult according to the opinion of the Rabbis, who hold that the New Moon of Sivan that year was on Monday.

The Gemara answers: The Rabbis could have said to you that a day was added to Iyyar that year and it was thirty days long. The New Moon was determined by testimony of witnesses who saw the new moon, together with astronomical calculations that the testimony was feasible. Therefore, Iyyar could be thirty days long. If that was the case, the New Moon of Sivan was on Monday. Come and hear an objection from what was taught in a different baraita that they did not add a day to Iyyar that year, as the Sages taught: In the month of Nisan during which the Jewish people left Egypt, on the fourteenth, they slaughtered their Paschal lambs; on the fifteenth, they left Egypt; and in the evening, the firstborn were stricken. The Gemara asks: Does it enter your mind to say that they were stricken in the evening? Was the Plague of the Firstborn after the Jews left Egypt? Rather, say that the evening before, the firstborn were stricken. And that day was the fifth day of the week. Nisan was complete, i.e., it was thirty days long, and the New Moon of Iyyar occurred on a Shabbat.

Iyyar was lacking, i.e., it was twenty-nine days long, and the New Moon of Sivan occurred on the first day of the week. This is difficult according to the opinion of the Rabbis. The Gemara answers: Whose is the opinion in this baraita? It is the opinion of Rabbi Yosei. Therefore, this baraita poses no difficulty to the opinion of the Rabbis.

Rav Pappa said: Come and hear a different proof from another verse, as it is stated: “And they took their journey from Elim, and all the congregation of the children of Israel came unto the wilderness of Sin, which is between Elim and Sinai, on the fifteenth day of the second month after their departing out of the land of Egypt” (Exodus 16:1). And that day was Shabbat, as it is written: “And in the morning, then you shall see the glory of the Lord; for He has heard your murmurings against the Lord; and what are we, that you murmur against us?” (Exodus 16:7). The next day the glory of God was revealed, and He told them that in the afternoon the manna and quail would begin to fall, and it is written: “Six days you shall gather it; but on the seventh day is Sabbath, there shall be none in it” (Exodus 16:26). Apparently, the first six days after this command were weekdays on which the manna fell, and the fifteenth of Iyyar was Shabbat. And from the fact that the fifteenth of Iyyar was Shabbat, the New Moon of Sivan was on the first day of the week. This is difficult according to the opinion of the Rabbis. The Gemara answers: According to the Rabbis, a day was added to Iyyar that year and it was thirty days long. Therefore, the New Moon of Sivan was on Monday.

Rav Ḥavivi from Ḥozena’a said to Rav Ashi: Come and hear a different proof from the following verse: “And it came to pass in the first month in the second year, on the first day of the month, that the Tabernacle was erected” (Exodus 40:17). It was taught: That day took ten crowns. It was the first day of Creation, meaning Sunday, the first day of the offerings brought by the princes, the first day of the priesthood, the first day of service in the Temple, the first time for the descent of fire onto the altar, the first time that consecrated foods were eaten, the first day of the resting of the Divine Presence upon the Jewish people, the first day that the Jewish people were blessed by the priests, and the first day of the prohibition to bring offerings on improvised altars. Once the Tabernacle was erected, it was prohibited to offer sacrifices elsewhere. And it was the first of the months. And from the fact that the New Moon of Nisan of that year was on the first day of the week, in the previous year, it was on the fourth day of the week.

As it was taught in a baraita, Aḥerim say: Between the festival of Assembly, i.e., Shavuot, of one year and the festival of Assembly of the following year, and similarly, between Rosh HaShana of one year and Rosh HaShana of the following year, there is only a difference of four days of the week. And if it was a leap year, there is a difference of five days between them. There are three hundred and fifty four days in a year, which are divided into twelve months, six months that are thirty days long and six months that are twenty-nine days long. If the New Moon of Nisan was on Wednesday, the New Moon of Iyyar was on Shabbat eve, and the New Moon of Sivan was on Shabbat. This is difficult both according to Rabbi Yosei, who holds that the New Moon of Sivan was on Sunday, and according to the Rabbis, who hold it was on Monday. The Gemara answers: Both Rabbi Yosei and the Rabbis disagree with Aḥerim. According to Rabbi Yosei, they established seven months that were lacking in the first year, i.e., seven months that were twenty-nine days long,