Changing the intention for fasting after dawn

A fasting intention made at night is considered valid. If a person has a definite intention to fast the next day, the fast will automatically begin at dawn (Subah Saadiq). Hence, if one does not continue the fast, Qadha is required.

A person may change their intention and choose not to fast before dawn. In this case, Qadha will not be required. However, once dawn breaks, the intention cannot be changed. [Hindiyyah 1: 195]

If a person were deliberating whether to fast and did not make a definite intention at night, the above would not apply. In this case, Qadha would not be required if the person chose not to fast.

And Allah Ta’ala Knows Best