Imam Abu Abdillah (as) was asked about a woman who woke up Fasting in the morning. So when the day rose, or it was the evening, she menstruated. Would she break [the fast]?
Imam (as) said: Yes, and even if it was the time of [just] before al Maghrib, so let her break.
[al Kafi, Volume no. 4]
Divine Treasure 