Then he, Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, said: "If a man knowingly has intercourse with his wife while she is menstruating, he has sinned." We have mentioned what has been narrated regarding the prohibition of intercourse with a menstruating woman, and whoever commits a prohibited act has sinned without any dispute. Then he, Shaykh (Al-Mufid), said: "And he must offer kaffarah (expiation). If the intercourse occurs during the beginning of menstruation, he must give a dinar equivalent to ten silver dirhams in value. If it occurs in the middle, he must expiate with half a dinar. If it is at the end of menstruation, he must expiate with a quarter of a dinar." This is supported by relevant evidence.
Commentary #12