He Committed Illegal Sexual Intercourse With a Woman and He Wishes to Marry Her

Question :

A man committed illegal sexual intercourse with a virgin and now he wishes to marry her; is it permissible for him to do so?

Answer:

If the matter is as described, it is incumbent upon both of them to turn to Allah in repentance, to abandon this sin, to show remorse for the sinful deed which they have committed, to make a firm commitment not to repeat it, and to perform many good deeds, that haply, Allah may turn to them with forgiveness and replace their evil deeds with good deeds. Allah, Most High says:
"And those who invoke not any other iläh (god) along with Allah, nor kill such person as Allah has forbidden, except for just cause, nor commit illegal sexual intercourse and whoever does this shall receive the punishment. The torment will be doubled to him on the Day of Resurrection, and he will ahide therein in disgrace; Except those who repent and believe (in Islamic Monotheism), and do righteous deeds; for those, Allah will change their sins into good deeds, and Allah is Oft-Forgiving, Most Merciful. And whosoever repents and does righteous good deeds; then verily, he repents towards Allah with true repentance."

And if he wishes to marry her, he must make sure that she is free from pregnancy by the occurrence of a menstrual period before he makes a marriage contract with her. If it becomes evident that she is pregnant, it is not permissible for him to marry her except after she delivers the child, in accordance with the Hadith in which the Prophet forbade a man from irrigating another man's crop with his water (i.e., his sperm).

And may peace and blessings be upon our Prophet, Muhammad and upon his family and Companions.

Source:
The Permanent Committee
Fatawa Islamiyah, Vol. 5 Pages 431-432