How is the duration of one month calculated for an oath sworn on the first day of the last third of August, and is it thirty days, or is it considered a full month with all its days?

If a person swears to abstain from something for a month, there are two scenarios:

The first scenario: If the oath was taken at the beginning of the month (at its crescent sighting), then they must abstain from that thing until the end of that month, determined by the sighting of the next crescent moon, whether the month is twenty-nine or thirty days. This is by the consensus of Muslims.

The second scenario: If the oath was taken during the month (in its middle), scholars have differed in determining the duration of the month:

1. The view of the majority: They must abstain for thirty days. 2. Another view: They must abstain for twenty-nine days, citing as evidence the Prophet's (peace and blessings be upon him) oath of ila' (abstention from his wives). 3. The view of Sheikh Ibn Taymiyyah and those who agreed with him: The month ends on the same day of the following month as the day the oath began, whether the first month was incomplete or complete. This is the correct view and what Muslims practice, based on the Almighty's saying: (Say, "They are fixed times for the people") and on understanding common custom in transactions.

The months considered in Islamic law are the lunar months, not the solar ones. In an oath, the intention of the swearer and common custom are taken into account.