What is the ruling on a husband having intercourse with his wife at the beginning of her menstruation without his knowledge, or unintentionally, where the intention was foreplay, or due to both spouses not knowing about the start of the menstrual cycle?

If a man has intercourse with his menstruating wife and they were unaware of her menstruation, or if menstruation occurred during intercourse, there is no sin upon them, based on the hadith: "My Ummah has been forgiven for mistakes, forgetfulness, and what they are forced to do." He must cease immediately upon realizing she is menstruating; otherwise, he incurs sin and the expiation (kaffarah) becomes obligatory (giving a dinar or half of it in charity). If the woman knows she is menstruating and her husband does not, she is sinful if she allows him. As for one who knows his wife is menstruating and intentionally engages in intercourse, he has sinned, and expiation becomes obligatory. His wife also sins if she complies, based on the Almighty's saying: "So keep away from women during menstruation." He should avoid anything between the navel and the knee during foreplay to prevent falling into the forbidden.