Could the 40th, or Arbaeen, of Imam Hussain (p) fall on the 19th or 20th of Safar given that the lunar month can be 29 or 30 days? Will the visitation (ziyarah) be fulfilled if the visitor cannot stay until the actual 40th? What if the visitation is to fulfill a vow?
It is hoped that the visitation will be fulfilled (i.e., the visitor will receive a special reward from God), even if it is performed before the 40th. The 40th of Imam Hussain (p) falls on the 20th of Safar; therefore, the vow would not be fulfilled unless the visitation is performed on the actual day of the 40th (i.e., the 20th of Safar).