Forbidden for you are your mothers, your daughters, your sisters, your paternal aunts, your maternal aunts, your brother's daughters, your sister's daughters, your foster-mothers who nursed you, your sisters through nursing, your wives' mothers, and your stepdaughters in your guardianship—born of wives you have gone into—but if you have not gone into them, there is no blame on you. And the wives of your genetic sons, and marrying two sisters simultaneously. Except what is past. God is Oft-Forgiving, Most Merciful.

The Holy Quran · An-Nisaa (The Women) · 4:23