The ruling on one who vowed to fast days in the month of Rajab, but the month ended and the month of Sha'ban arrived

Question : The questioner says: Honorable Shaykh, a man vowed to fast three days in Rajab. He completed fasting two days, but he forgot the third day and remembered it in the month of Sha'ban. What is the ruling?

Answer : The ruling for one who vowed to fast three days in Rajab, then forgot and fasted only two days, so the month ended, is that he must fast the remaining days and expiate with the expiation for an oath, because the time for the vow has passed.