سنن النسائي

It was narrated from 'Amrah that 'Aishah told her that the Messenger of Allah (ﷺ) was with her, and she heard a man asking permission to enter Hafsah's house. 'Aishah said: "I said: 'O Messenger of Allah, there is a man asking permission to enter your house.' The Messenger of Allah (ﷺ) said: 'I think it is so-and-so the paternal uncle of Hafsah through breast-feeding.' 'Aishah said: If so-and-so (her own paternal uncle through breast-feeding) were alive, would he be allowed to enter upon me?' The Messenger of Allah (ﷺ) said: 'What becomes unlawful (for marriage) through breast-feeding is that which becomes unlawful through birth.'"