What is the ruling on one who swears to fast a specific number of days if he commits a sin, but contents himself with fasting three days as expiation for his oath each time?

Frequent swearing is forbidden in Islamic law because it exposes the swearer to breaking an oath. If a Muslim swears to abandon a sin, it is recommended for him to fast the days he swore to. If he does not fast them, the expiation for breaking an oath becomes obligatory upon him, which is feeding ten needy persons, or clothing them, or freeing a slave. If he is unable to do that, then fasting three days.

He must also cease committing that sin. If there are multiple oaths with a single cause, and he breaks them before expiating, then only one expiation is due. However, if he breaks a single oath and expiates for it, then swears another oath, a second expiation becomes obligatory upon him, and so on.