שולחן ערוך אורח חיים · סימן תכ״ז

English

How documents are dated when Rosh Chodesh falls on two days. Contains one section When Rosh Chodesh falls on two days, documents written on the first day are dated "on Rosh Chodesh" which is the thirtieth day of the previous month. Rema: The month is counted from the second day and documents written on it are dated the first of the month. When the year is intercalated, the first Adar is written simply as "Adar" and the second is written as "Adar the Second."