Purity: Mistaken Identification of Hayd

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 496:

If a woman considers her bleeding on some days to be ḥayḍ and does not perform ritual acts of worship, and afterwards she realises that it was not ḥayḍ, she must make up the prayers and fasts that she missed on those days. If she worships on some days supposing that her bleeding on those days is not ḥayḍ, and afterwards she realises that it was ḥayḍ, then in the event that she had also kept obligatory fasts on those days, she must make them up.

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