What is the ruling on one who swore an oath upon the Qur’an not to return to committing a sin, and then returned to it?

Adultery is one of the major sins and abominable acts. The oath to abandon it is binding, whether it was sworn on the Qur’an or not, and it must be fulfilled. Whoever violates their oath must offer sincere repentance and perform an expiation for the oath, which is feeding ten poor people, or clothing them, or emancipating a slave. If one is unable to do so, then fasting for three days. Advising and warning a friend is obligatory, but if he insists on committing the abominable act, then there is no good in his companionship.