Last Ramadhaan, I was menstruating, and on the last day of my menstruation, I had my Sahoor (pre-dawn meal) and had the intention of fasting. No blood discharge occurred during the day and I completed my fasting until sunset. However, I did not perform Ghusl except at the time of the Maghrib prayer. What is the Sharee‘ah ruling on this? Is my fasting that day valid?

All perfect praise be to Allaah, the Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

If your menstruation ended before the crack of dawn, then your fasting that day would be valid. Delaying Ghusl after being pure from menstruation does not invalidate fasting. Nevertheless, it was incumbent upon you to perform Ghusl immediately after seeing the sign of purity in order to perform the obligatory prayers at their due time.

You are required to make up for the Maghrib and ‘Ishaa’ prayers of that day if your menstruation had stopped before dawn and there was enough time to perform Ghusl and perform these two prayers. You are also required to make up for the other prayers of that day: the Fajr, Thuhr and ‘Asr prayers.

You are also required to return back to Allaah and repent from that sin, which was to deliberately delay prayers after their due time.

If your menstruation stopped after the crack of dawn, fasting that day would be invalid and you would be required to make up for it. 

And Allaah Knows best.