Does fosterage prohibit the same relations as kinship?
Chapter on What is Prohibited to Marry and Combining Between Them and Other Matters
Al-Mughni
Book of Marriage
Primary text
Fosterage prohibits the same relations as kinship: mothers, daughters, sisters, paternal aunts, maternal aunts, daughters of the brother, and daughters of the sister, based on the narration, "Fosterage prohibits what lineage prohibits" (Muttafaq 'Alayh), and in another narration, "Fosterage prohibits what birth prohibits" (Muslim). The prohibition of mothers and foster-sisters is explicitly textual, while the rest fall under the general scope of other forbidden relatives mentioned in the text.
Supporting text
The majority of scholars agree that fosterage prohibits the same relations as kinship. Some innovators, specifically the Rafidah and Khawarij, do not uphold this prohibition or the established Sunnah concerning combining sisters.