Purity: Fasting and Istiḥāḍah After ʿAṣr Prayer

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 417:

If a fasting woman becomes mustaḥāḍah after ʿaṣr prayers and she does not perform ghusl until sunset (ghurūb), her fast is valid without any problem.

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