Having intercourse with one's wife without knowing that she is in her menses

Q 2: What is the ruling on a man who had sexual intercourse with his wife and only knew she was menstruating after they had sex?

A: Any man who has sexual intercourse with his wife without knowing that she is having her menses is not a sinner, but he should offer Kaffarah (expiation), which is to give as Sadaqah (voluntary charity) one or half a Dinar (old Arab coin that equals 2.975 grams of gold) of gold. This is based on the general rule stated by Prophet (peace be upon him), who said: Anyone who has sexual intercourse with his wife during her menses should give a Dinar or half a Dinar as Sadaqah. (Related by Imam Ahmad and the Four Compilers of Hadith through a Sahih [authentic] Sanad [chain of narrators]) Any menstruating woman should hint to her husband that she is having her menses.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.