Introducing a new rule in the fixation of the molad (lunar conjunction) of the month of Tishri, Ben Meïr in 921 CE decreed that, in the year 922, Passover and the other Jewish feasts should be celebrated two days before the date prescribed by the traditional calendar.
A letter from the exilarch David ben Zakkai and the Babylonian notables was sent to ben Meïr, imploring him not to cause a schism and showing him the fallacy of his calculations with regard to the calendar.