Answer
Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
No, Islam strictly prohibits a woman from marrying her stepson. This ruling is based on clear Qur’anic instruction, which considers such a union immoral and harmful to family structure.
Answering your question, Dr. Mohammad S. Alrahawan, Associate Professor at the department of Islamic Studies in English, Al-Azhar University, Egypt, states:
According to the Islamic Shari`ah, a woman is prohibited to get married to her stepson. We read in the Qur’an what means:
“And do not marry those [women] whom your fathers married, except what has already occurred. Indeed, it was an immorality and hateful [to Allah] and was evil as a way.” (An-Nisaa’ 4:22)
Allah Almighty knows best.