What is the ruling on a husband having intercourse with his wife after her lochial bleeding has stopped, but before forty days have passed, and then bleeding appears after the intercourse—is it menstrual blood or lochial blood?

There is no sin upon the husband for engaging in intercourse with his wife during her purity from nifas (postnatal bleeding), even if it is before the forty days. However, if the bleeding returns before the completion of the forty days, it is still nifas blood, and she must refrain from what a woman in nifas refrains from until she becomes pure or the forty days are exceeded.