Purity: Intercourse During Days of Uncertain but Assumed Ḥayḍ

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 449:

Sexual intercourse is unlawful on the days when even though ḥayḍ is not certain, the woman must still regard herself as being ḥāʾiḍ. Therefore, a husband cannot have intercourse with his wife on the days when she experiences bleeding for more than ten days and who must – according to the instructions that will be mentioned later – regard the days of her close relatives’ habitual pattern as her ḥayḍ days.

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