Fasting: Invalidating a Qadaʾ Fast Before Zuhr
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1669
One can invalidate the qaḍāʾ fast of the month of Ramadan before ẓuhr. However, if the number of days left for him to keep his qaḍāʾ fasts [before the start of the month of Ramadan] are few, it is better that he does not invalidate them.