Who are the women unlawful for marriage?

Women are of two types: those permanently prohibited (for marriage) and those temporarily prohibited due to a removable cause. Those permanently prohibited are mentioned in An-Nisa’ (4:23) and in the Hadith (definition), "What is prohibited by fosterage is what is prohibited by lineage." The verse specifies those prohibited by lineage: mothers, daughters, sisters, paternal aunts, maternal aunts, nieces (daughters of brothers), and nieces (daughters of sisters). Thus, a man is prohibited from marrying his ascendants, his descendants, the descendants of his first ascendants, and the first descendant of every ascendant thereafter. Likewise, seven types of women are prohibited by cause: two by fosterage, four by affinity (marriage), and the seventh being chaste women (already married). Those prohibited by fosterage are the same as those mentioned in the verse, and what is prohibited by fosterage is what is prohibited by lineage, under two conditions: that it occurs within the first two years of life, and that there are five known sucklings. As for those prohibited by affinity, they are: the mothers of wives, and stepdaughters provided that intercourse has occurred with the mother, and the wives of sons. It is also prohibited to combine (in marriage) two sisters, or a woman and her paternal aunt, or a woman and her maternal aunt. Marriage to a woman who has been subjected to li'an (mutual imprecation) is also permanently prohibited.