Fasting: Intentionally Breaking a Fast Followed by a Legitimate Excuse
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1644
If a person intentionally breaks his fast and afterwards a legitimate excuse arises – such as ḥayḍ, nifās, or an illness – the recommended precaution is that he should give kaffārah, especially if some medication or other such means brought about the ḥayḍ or illness.