Sahih Muslim Book 8, Hadith Number 3271.

Chapter: It is forbidden to combine a woman and her father’s sister or a woman and her mother’s sister together in marriage.

Abu Huraira (Allah be pleased with him) reported that Allah’s Messenger (May peace be upon him) forbade a person to combine in marriage a woman and her father’s sister, and a woman and her mother’s sister. Ibn Shihab said: So we regarded the paternal aunt of her (wife’s) father and the maternal aunt of her (wife’s) father at the same level.