Sayyidah Aishah (may Allah be pleased with her) narrates from the Messenger of Allah (peace and blessings be upon him) that the Messenger of Allah (peace and blessings be upon him) was asked about a man who commits zina with a woman: may he marry her daughter? Or who commits zina with her daughter: may he then marry her mother? The Messenger of Allah (peace and blessings be upon him) said: "The unlawful does not make the lawful unlawful; only what was through a lawful marriage makes (things) unlawful." Ishaq said: Abdullah bin Nafi' said: And this is what we adopt.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13966