Fasting two consecutive months by the sighting of the moon or by the number of days

Question:
And the Shaykh (may Allah have mercy on him) [asked]: If a person is required to fast two months, does the shortfall in the month count toward it, if the month lasts twenty-nine days, or is he required to fast sixty consecutive days?

Answer:
If he starts from the sighting of the moon, he is required to fast a lunar month, whether it is full or short. However, if he starts in the middle of the month, he must fast by the number of days; sixty days are required. This is the distinction: if he starts from the sighting of the moon, he is required to fast a lunar month, whether it is full or short. But if he starts in the middle of the month, sixty days are required. Yes.