What is the ruling on a husband having intercourse with his wife during the period of nifas after the bleeding has stopped, and then bleeding appears after the intercourse?

If a husband has intercourse with his wife after her postpartum bleeding (nifas) has stopped but before she has performed the ritual bath (ghusl), he is sinful. However, according to the more preponderant opinion, he is not required to offer expiation (kaffarah); seeking forgiveness (istighfar) and repentance suffice for him. But if he has intercourse with her after the bleeding has stopped and she has performed the ritual bath, there is no sin upon him, even if the bleeding returns.