Sahih Bukhari

Narrated `Aisha:My foster uncle came and asked permission (to enter) but I refused to admit him till I asked Allah's Apostle about that. He said, ""He is your uncle, so allow him to come in."" I said, ""O Allah's Messenger (ﷺ)! I have been suckled by a woman and not by a man."" Allah's Messenger (ﷺ) said, ""He is your uncle, so let him enter upon you."" And that happened after the order of Al-Hijab (compulsory veiling) was revealed. All things which become unlawful because of blood relations are unlawful because of the corresponding foster suckling relations