Is a husband sinful if he has intercourse with his wife, believing that the blood coming from her is due to a membrane covering the ovum and not menstrual blood, knowing that the treatment will continue for three months?

It is forbidden for a man to have intercourse with his wife while she is menstruating. However, intermenstrual bleeding (istihada) does not prevent intercourse.

If you had intercourse with your wife, believing her to be ritually pure from menstruation, there is no sin upon you, for the Prophet, peace and blessings be upon him, said: "Indeed, Allah has forgiven my nation for mistakes, forgetfulness, and what they are compelled to do."

Giving a dinar or half a dinar in charity is more cautious and absolves one's responsibility. The weight of a dinar is approximately four and a quarter grams of gold.