Purity: Doubt Between Ḥayḍ and Istiḥāḍah

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 445:

If a woman experiences bleeding and doubts whether it is ḥayḍ or istiḥāḍah, in the event that it has the conditions of ḥayḍ, it must be considered to be ḥayḍ.

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