What is the ruling regarding a husband having intercourse with his wife after she saw a pinpoint-sized spot of blood, and before she could ascertain whether this blood was menstrual blood, given that the blood flowed after intercourse, and what is the expiation for this sin?

Any blood found that is not considered menstruation by the majority of scholars necessitates making up the Asr, Maghrib, and Isha prayers. The intercourse that occurred before the discovery of menstruation is not sinful, because the event is attributed to its nearest time. Menstruation is not considered to exist legally إلا by the emission of blood, or yellowish or brownish discharge during the usual menstrual period, and not merely by the sensation of pain.