Chapter 18: The Book of Suckling
' A' isha (Allah be pleased with her) reported tha Allah' s Messenger (ﷺ) was with her and she heard the voice of a person seeking permission to enter the house of Hafsa. 'A' isha (Allah he pleased with her) said: Allah' s Messenger, he is the person who seeks permission to enter your house, whereupon Allah' s Messenger (ﷺ) said: I think he is so and so (uncle of Hafsa by reason of fosterage). 'A' isha said: Messenger of Allah, if so and so (her uncle by reason of fosterage) were alive, could he enter my house? Allah' s Messenger (ﷺ) said: Yes. Fosterage makes unlawful what consanguinity makes unlawful.
Sahih Muslim 1444a