Is the intercourse that occurred with the wife while she was seeing blood, which she initially thought was istihadah (non-menstrual vaginal bleeding) but later turned out to be menstruation, considered a sin requiring repentance? And what is the authenticity of the hadith narrated from the Prophet, may Allah’s prayers and peace be upon him and his family: "Whoever has intercourse with his wife while she is menstruating, and the child is born leprous or with vitiligo, let him blame no one but himself"?

This blood is considered menses if it occurs at a time suitable for it. As long as you did not intentionally engage in intercourse and believed that this was not menstruation, there is no sin upon you. Muslims have unanimously agreed on the prohibition of intercourse with a menstruating woman. If one does so out of ignorance of the presence of menstruation or its prohibition, or out of forgetfulness or compulsion, there is no sin upon them and no expiation. As for the mentioned hadith, it is not found except in the books of the people of innovation.