(20) بَابُ: {وَأُمَّهَاتُكُمُ اللاَّتِي أَرْضَعْنَكُمْ}
Narrated `Aisha:
(the wife of the Prophet) that while Allah's Messenger (ﷺ) was with her, she heard a voice of a man asking permission to enter the house of Hafsa. `Aisha added: I said, "O Allah's Messenger (ﷺ)! This man is asking permission to enter your house." The Prophet (ﷺ) said, "I think he is so-and-so," naming the foster-uncle of Hafsa. `Aisha said, "If so-and-so," naming her foster uncle, "were living, could he enter upon me?" The Prophet (ﷺ) said, "Yes, for foster suckling relations make all those things unlawful which are unlawful through corresponding birth (blood) relations."
Reference: Sahih al-Bukhari 5099
In-book reference: Book 67, Hadith 37
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 7, Book 62, Hadith 36