It is narrated from Umrah bint Abdul Rahman that the wife of the Prophet ﷺ, Aisha (may Allah be pleased with her), told her that the Prophet ﷺ was sitting with her when she heard the voice of a man who was seeking permission from Hafsa (may Allah be pleased with her). Aisha (may Allah be pleased with her) said: "O Messenger of Allah ﷺ! This man is asking permission to enter your house." The Messenger of Allah ﷺ said: "I think this is so-and-so" (he mentioned the name of Hafsa's foster uncle). So I asked: "If so-and-so, who was her foster uncle, were alive, could he come to me?" The Messenger of Allah ﷺ said: "Yes, just as blood relations make something unlawful (for marriage), so does suckling (breastfeeding) establish prohibition."
Hadith Referenceمسند الإمام الشافعي / كتاب النكاح / 1177
Hadith Takhrijاخرجه البخاري الشهادات ، باب الشهادة على الانساب والرضاع .... الخ (2646)، (3105)۔ ومسلم، الرضاع، باب يحرم من الرضاعة ما يحرم من الولادة (1444)۔