I asked Imam (as) about a man who committed fornication with a woman and then later wanted to marry her. Imam (as) said: "If she repents, she becomes lawful for him." I asked: "And how can her repentance be known?" Imam (as) replied: "He should invite her to engage in the same unlawful act they previously committed. If she refuses and seeks forgiveness from her Lord (azj), then her repentance is known."