How can a man atone for the sin of having intercourse with his fiancée before marriage?

The engagement is merely a promise of marriage and does not permit the suitor to be alone with his fiancée, for he is a stranger to her. Negligence in this regard can lead to committing adultery. In such a case, marriage is not valid until after repentance and the clearing of the womb. This is the view of the majority of scholars. However, the Hanafis and Shafi'is hold that the marriage of those who committed adultery is valid even before repentance and the clearing of the womb. Since the marriage has already taken place, there is no harm in adopting the view of the Hanafis and Shafi'is regarding its validity, along with the obligation to hasten in sincere repentance from the immoral act. Repentance involves abandoning the sin, regretting it, resolving not to return to it, concealing one's own sin, and striving in righteous deeds.