Is it forbidden for a man to marry his sister (including sister from Zina)?
Chapter on What is Prohibited to Marry and Combining Between Them and Other Matters
Al-Mughni
Book of Marriage
Primary text
It is forbidden for a man to marry his sister, and also his sister born from adultery (*Zina*). This is the position held by the majority of jurists. The prohibition is based on the clear injunction found in the Quran: "Forbidden to you are your mothers and your daughters..." (Quran 4:23), which encompasses all forms of familial prohibition, although the specific textual basis for the sister is derived from the established scope of prohibited relatives.
Supporting text
Malik and the established opinion of Al-Shafi'i permit marriage to the daughter of adultery, based on the premise that she is considered an unrelated stranger (*ajnabiyyah*).