Answered by Shaykh Yusuf Weltch
Question
What is the ruling regarding having intercourse after the menstruation ends but before the ghusl?
Answer
In the Name of Allah, the Most Merciful and Compassionate
Allah Most High says, “They ask you (O Muhammad) concerning menstruation. Say: ‘It is a harm; so avoid (intercourse with) women during menstruation and do not approach them till they be cleaned. When they are thus purified, then you may go unto them as Allah has commanded you.’ Verily, Allah loves those who repent constantly, and (He) loves those who purify themselves.” [Quran, 2:222]
For this, it is strictly prohibited to engage in intercourse during the menstruation and even after the menstruation but before the ghusl unless the menstruation ended at the completion of the maximum period length of ten days. [Shurunbulali, Maraqi al-Falah]
Given that the intercourse during menstruation was unintentional, it wasn’t sinful. However, it is recommended to give the equivalent of a Dinar or half of a Dinar in charity as expiation. [Shurunbulali, Maraqi al-Falah]
A Dinar is equivalent to 4.25 grams of gold (Appx. $230 USD) and the Half Dinar is equal to 2.125 gram (appx. $115 USD). [Birgivi’s Manual Interpreted]
Hope this helps
Allah knows best
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani