Purity: Preventing Blood Flow During Continuous Istiḥāḍah
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 413:
If the blood of a mustaḥāḍah is continuous and does not stop, in the event that it is not harmful for her, she must, based on obligatory precaution, prevent the blood from coming out before performing ghusl. In the event that she is negligent in doing this and blood comes out, and she has performed prayers, she must perform them again. And the recommended precaution is that she should perform ghusl again [before performing these prayers].
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)