Letter: T-S 8G7.1

. . . that we and all Israel be [one] band [in all] months and all festivals. This custom has been followed by our fathers and by the yeshivot until now, which is the year 1147 of the Seleucid era, and the year 4595 from the Creation. Although as regards Marḥeshwan, Kislew and Tevet, their moon [will be] delayed, nevertheless—since the moon of Nisan is to be born in the daytime of the third [day] of the week [Tuesday] at four hours—if the [months of 835/6 CE] were intercalated and made full, then the beginning of Nisan would be set on the fifth [Thursday], whereas [the new moon] would be visible in the West before the beginning of the month, and [hence] this matter [the calendar] would be disrupted. And it is impossible to make [the months of 835/6 CE] regular, for then Pesaḥ would occur on the fourth of the week [Wednesday], and [this would contravene] lo BaDU Pesaḥ. And why lo BaDU Pesaḥ and lo GaHaZ ‘Atzeret? Because lo ADU Rosh ha-Shanah. For if we make Pesaḥ on the second of the week, the new year occurs on the fourth, and the Day of Atonement on Friday, and this is impossible because of the dead. 

verso

And if we make Pesaḥ on the fourth, the new year occurs on Friday, and the Day of Atonement on the first of the week, and this is impossible because of having to leave the dead unburied for two days of sabbath rest. And if we make Pesaḥ on Friday, the new year occurs on the first of the week, and this is impossible because of the great festival of the Willow—the Willow should not occur on the Sabbath. Thus we can only make the months [of 835/6 CE] defective, so that in Nisan, the new moon be not disrupted. And this applies not only in this present case, where they have so decided and . . . before the head of the ḥavurah and its members [that the months shall be] defective—for [in this case] we rely on them [the assembly] because it is impossible to make them [the months of 835/6 CE] regular or full, but even when it makes no difference whether [the months] are made regular, full, or defective, we always rely on them [the ḥavurah], lest Israel be split into factions. I, the heads of the yeshivot, the rabbis, and all Israel, rely [?]‌ on the calendar that was sent from before the ḥaverin . . . as they said before . . . they fear heaven.