What is the ruling regarding a man having sexual intercourse with his wife, thinking she is pure, only to find out later that she was in the first days of her menstruation, knowing that the blood was flowing from her due to the insertion of an IUD?

The basic rule regarding blood discharged from a woman's vagina is that it is menstrual blood, and she must refrain from prayer, intercourse, and other acts as soon as she sees it. It is not considered dysfunctional bleeding (istihadha) unless it continues for more than fifteen days, or if it appears before fifteen days have passed since her previous period of purity. If the blood the sister saw was not istihadha, then she and her husband erred by having intercourse if they were aware of the blood and its ruling, and they must repent. However, if they were ignorant of this, we hope there is no sin upon them for what has passed, and they must avoid this in the future.