Sunan Sa'id

His (Allah's) saying: {Forbidden to you [for marriage] are your mothers, your daughters, your sisters, your paternal aunts, your maternal aunts, daughters of your brother, daughters of your sister, your milk-mothers who nursed you, your milk-sisters, mothers of your wives, your stepdaughters under your guardianship [born] of your wives unto whom you have gone in—but if you have not gone in unto them, there is no sin upon you—and the wives of your sons who are from your loins, and that you take [in marriage] two sisters simultaneously, except for what has already occurred. Indeed, Allah is ever Forgiving and Merciful}