Purity: Bleeding Twice in One Month

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 492:

If a woman who usually experiences bleeding once a month experiences bleeding twice in one month, then in the event that the number of days on which her bleeding stops in between is not less than ten, she must consider both bleedings to be ḥayḍ even if one of them does not have the attributes of ḥayḍ.

-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)