Is it permissible for a man to marry a woman with whom he had an illicit relationship after both of them have repented, and if it is not permissible, what is the solution for those who have become involved in such a relationship?

The marriage of two fornicators after their repentance is permissible; indeed, it is more conducive to cutting off the path of Satan. This is supported by the hadith: "There is nothing like marriage for two who love each other." This is the view of the four Imams and many of the early Muslims (Salaf). For the sake of "istibra'" (ensuring the absence of pregnancy), it is a condition that if she is pregnant, she must give birth, or if she is not pregnant, she must experience one menstrual cycle, based on the Prophet's (peace be upon him) saying: "A pregnant woman should not be approached (for intercourse) until she gives birth, nor a non-pregnant woman until she menstruates once."