Gennadius. Lives of Illustrious Men 7

Pachomius the monk, a man endowed with apostolic grace both in teaching and in performing miracles, and founder of the Egyptian monasteries, wrote an Order of discipline suited to both classes of monks, which he received by angelic dictation. He wrote letters also to the associated bishops of his district, in an alphabet concealed by mystic sacraments so as to surpass customary human knowledge and only manifest to those of special grace or desert, that is To the Abbot Cornelius one, To the Abbot Syrus one, and one To the heads of all monasteries exhorting that, gathered together to one very ancient monastery which is called in the Egyptian language Bau, they should celebrate the day of the Passover together as by everlasting law. He urged likewise in another letter that on the day of remission, which is celebrated in the month of August, the chief bishops should be gathered together to one place, and wrote one other letter to the brethren who had been sent to work outside the monasteries.