Fasting: Interrupting a Continuous Fast with a Legitimate Excuse
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1634
If during the days that someone must fast continuously a legitimate excuse arises – such as ḥayḍ, nifās, or a journey on which he has to go – then once the excuse expires, it is not obligatory for him to start the fasts all over again; rather, he will continue the rest of the fasts immediately after the excuse has expired.